A few theorems of design

Banana split: sensory bombardment
We humanoid life forms love to bombard our senses. The more the better - the experience seems heightened the moire sensory receptors we can excite. Examples: An ice cream sundae with vanilla ice cream, hot fudge, salted pecans, whipped cream, and a cherry has sweet and salty, hot and cold, creamy and crunchy, and light and dark. Um, we love it. A hamburger with 'the works' has hot and cold, crunchy and soft, sweet and salty, tart and smooth, and more. And we like it when it has the variety to excite more of our senses.
However, all the ingredients need to be in balance, if there is too much mustard, it throws off the balance of the burger and we are not so enthralled. In design, keep in mind that the reader/viewer may like a more sensory experience, but elements need to be in balance.

Freeway passing: personal pace
Many of us, probly you included, will change lanes to get around someone who is impeding our progress. We realize its not to get to the light or the off-ramp first (it's not a competition), we just prefer to drive, or walk, at our own personal pace. We find comfort and confidence when we feel in control of the pace at which we operate in chaos. Freeways, especially rush-hour freeways are great equalizers - they take hundreds of individuals operating at different speeds and rhythm and require each of them to move at the exact same pace as everyone around them. As soon as we break free of the slow-down, we zip back to our preferred personal speed. Designers acknowledge that when they group all the readers/viewers into a group that reads the same words and sees the same images.

Target spill
An ad or piece of graphic design is aimed at a specific group of people. But sometimes, people on the fringe edges of that target audience are also paying attention and processing the message. the message may not be written or aimed at them, but they are receiving and responding to it just the same. Example: men/women watch feminine/masculine hygiene ads on media. Sometimes this spill into other demographics can create a negative response that is carried over into the intended audience. Designers and copywriters need to be cautious of the unintended audience to their work and will it have a detrimental effect.

Too close for comfort
I suspect that you have been in a friend's house and noticed that a picture on the wall was a bit crooked (above left). It probly annoyed your sense of order. If an object is aligned with other elements (right) or at an angle that is clearly intentional (middle), we are more comfortable with it. But when it is off just a bit, well, that is too close for comfort. Many of us cause a diversion and go straighten the offending object.

Ease on down: smooth transition
Every day presents new challenges and barbs to our desired plan and flow for the day. Sometimes, these influences switch from abruptly from one to the next. The day goes better, the message can be clearer, and the design work can be more effective if the designer considers these jerky movements and seek to make the transitions as smooth as possible. Unless, the desired effect is one of jarring disjointedness. Frank Lloyd Wright was a genius at guiding the visitors to his structures from their street position to a destination within the structure. Often we have experienced the structure without even being aware of how we were manipulated through the space. For more effective persuasion, it is better to take the target reader/viewer by the hand and walk them to where you want them to be, rather than yelling at them from across the room to get over here.

Familiar innovation
All design decision are compromises - actually, all decisions are compromises. To gain something, you have to give up something. Sometimes, its an easy choice, because its 90 versus 10, other times its tough: 50 versus 50. In design decisions, we often are deciding between what is familiar - that which requires very little education to communicate to the reader - and what is innovative - what is likely new and needing some processing and understanding.
• If a design decision is mostly or totally familiar, it will likely be ineffective because it is boring and mundane - there is no new stimulus to excite the mind of the viewer.
• If a decision is mostly or totally innovative, it runs the risk of not reaching the reader's mind because it may require too much work to accept.

Grand foyer: building confidence
I suspect you have walked into an unfamiliar space and paused to 'get your bearings'. We seem to have a need to survey new surroundings. It might be traced back to our tribal efforts to gain a defensive or offensive advantage when in a new place. This still holds true today - maybe not for strategic reasons, but for comfort. First impressions really do matter. Once our mind has established a judgment or attitude about something new, that becomes pretty solid in our memory. PR and Advertising people use this to their advantage to cement a notion in our minds.

Blinking stoplight: user education
When a city or town installs a stoplight at an intersection where there used to be a stop sign, or no sign at all, the new stoplight flashes yellow (or red) for a week or so. This gets the attention of the motorists and helps educate them to the new system in place. If the stoplight was installed and put into operation immediately, the traffic that used to have the right of way might run through the light out of habit. When introducing new info or a new system or a new procedure, there must be a period of educating the user. We get used to routines and form habits. The new format has to break us of our habit and introduce something new for us to process. The length of time for the education period will vary depending on the disruption of the norm and the complexity of the new info.

Order in the court: comfort of order
There is not much we can agree on as unique individual carbon life forms. But the vast majority of us agree that we do prefer a sense of order. Clear order or organization helps us navigate through the clutter of life, modern environments, and media. Once we accept a foundation of order, it allows us to move into new territory in the environment or in our minds. It seems important for the designer to establish a basis of order before moving the reader into new territory.

Figure out what's working; exploit that and minimize the rest. Strong messages can often be more effective if there is one major concept for the reader/viewer to grasp. Once the designer has determined that one strong message, then that should be the focus of the energy of clear communication. The word exploit works well here because it conveys grabbing, wrestling and pushing to the limits.

Artificial authenticity
In the movies, when they show someone looking through a pair of binoculars, they show us 2 overlapping discs representing the 2 barrels of the binoculars. That is what we expect to see and it is what we have seen in almost every film that shows a binocular view. But, the reality is that when one looks through binoculars, the 2 images merge into a single circle of the view. But the truth would not communicate as clearly to the audience. They stretch (or lie) to the authentic to become artificial. And, for them, it works.
Another: smartphones include a digital click to help us accept the new camera - we became used to the shutter click and felt cheated when our new camera had no such satisfying click.

Seduction of technology: theory
We become enamored by the 'coolness' of the latest new device, app, or system and sometimes forget what we had set out to do. The focus of our work can be overshadowed by how well the tech seduces us into playing and accommodating the object rather than the idea. Unfortunately, many of us push the function and benefit of the new tech to the back and concern ourselves with the flash and gimmick that has purposefully been integrated into the tech to entice us in.

Clarity, not simplicity
Effective Graphic Design is rarely about making something simple. Graphic Design is about making a message clearer. One way to achieve clarity is often to make it simpler. But simplicity is not the the objective, clarity is. Clarity can be achieved by improving many elements: contrast, color, placement, size, etc.

A few theorems from other sources

Shirky Principle
An entity can become so dedicated to solving a problem that it inadvertently perpetuates the problem.
Unions were a solution to the problem of management which exploited workers. But as capital increased in complexity, unions complexified as well, until unions needed management. Unions now perpetuate the problem (management) they are the solution to because as long as unions exist, companies feel they need management to offset them.

Disruptive technologies arise from the margins of an industry.
Honda's electric bicycles were no threat to the big four automobile companies, until electric bikes become motorcycles and motorcycles became small efficient cars. Cheap crummy dot matrix printers were no threat to big offset printing companies until dot matrix became inkjet printers and inkjets became big on-demand printers. The solutions were first marginal, barely working, and therefore ignored. Established industries like to focus on established problems.

Publish-then-filter is necessary due to the size and amount of material being created daily.
Social tools remove older obstacles to public expression, and thus remove the bottlenecks that characterized mass media. The result is the mass amateurization of efforts previously reserved for media professionals. Combined with the lowering of costs of creating content, mass amateurization of publishing changes the question from "Why publish this?" to "Why not?" The wiki concept that inspired Wikipedia is an example of this marriage of mass content creation and mass filtering.

The more ideas in circulation, the more ideas there are to disagree with.
Many advancements in communication throughout history, from the printing press to the television, were heralded as harbingers of world peace yet ended up creating greater dissent. However, with this increased arguing, comes an increased speed of information exchange. Audiences are built, communities grow, and participation matters more than quality.

Peter Principle
A person in an organization will be promoted to the level of their incompetence.
At that point their past achievements will prevent them from being fired, but their incompetence at this new level will prevent them from being promoted again, so they stagnate in their incompetence.