The human ability to exhibit powers and to what degree is proportionally related to their ability to focus. This is the primary reason why humans do not exhibit their maximum powers in every regard at all times. The partner of Focus Theory is Familiar Theory. Fundamentally, those abilities and things which one is most familiar with will be the easiest to Focus upon or use less focus.
Evidence
1. "You have to focus, Trinity."
2. Obvious and evident concentration on Neo's face bending the spoon, firing chain gun, etc.
3. Morpheous' posturing prior to exiting through the wet wall.
4. Et al - other moments of concentration and undisrupted focus.
5. Analogous to Special Relativity (exceptional cases can be explained by exceptional Focus).
6. Focus Meter in Enter The Matrix.
Specific Elements of Focus
Generally speaking, some level of Focus enables all abilities. So the question is, what comprises Focus or amplifies its ability to work. The two elements most evident to us is Freedom of the Mind and Awareness. The first is considered a lack of elements which bind the mind down- past experience, fear, doubt, uncertainty, etc. The second is a set of things which constrain the mind in the RIGHT direction. A monk, for example, will be Free of the belief that he cannot levitate and Aware there is more to this world beyond what he can see... as such he can Focus- Self-Editing himself to then levitate. Being Unplugged GREATLY contributes to Freedom and Awareness which is why Zionists are generally more capable of super-human feats. Potentials, being young, would have an equal amount of Awareness but less constraints on their Freedom... thus exhibiting abilities even beyond your average Zionist.
Objections
One is with the theory the other is with the application:
1. The One doesn't seem to need to focus. Potentially. Actually some events that The One does can be explained by Focus Theory. To see how it works out, check on Neo's Powers.
2. This is my own objection. Focus Theory is too much of a catch all and extremely ambiguous. Focus can be used to explain almost everything without exception while measuring the actual focus of a character nigh impossible. As such, Focus is very analogous to Special Relativity... so we will invoke it only as necessary. True, Relativity is always at work, but we generally ignore it- opting for Newtonian physics- until approaching lightspeed, similarly, we will stick to other Theories unless on the fringes of power theory.