A programming principle should only be followed when it provides more long-term benefit than any alternative. This may seem self-evident; it should be apparent from the fact that a principle that doesn’t provide long-term benefit obviously isn’t a good principle.

This is something that mediocre problem-solvers don’t always understand: deviation from generally accepted principle can be a sign of weakness or, contrarily, a sign of strength.

To take an analogy, in chess it is said that a rook is worth five, a bishop three, and a pawn one and so on. These facts aren’t anywhere in the rules of chess, they are just very good approximations, overall, that emerge from the game. About 90% of the time, you can use math based on these numbers to make good decisions.

However, 10% of the time other situation factors supersede this principle. Though there is an appeal to such simplicity, as one becomes closer to a master of chess he must let go of these numbers and move to a more advanced situation calculus. The same applies to coding.

Even the purest of coding principles have exceptions: though you’ve probably never considered it, every time you copy-paste you participate in a violation of DRY.

I’d like to reiterate, every single (non-trivial) coding principle necessarily has an exception. Why? Because every principle incurs a cost of a situation benefit. And for any such principle we can imagine a scenario, however unlikely, where the situationality of that benefit is totally avoided.

There is only one universal principle of problem-solving: the cost-benefit analysis. Every other principles only offer value as heuristic approximations. This is the calculus by which an expert must weigh the relevance and generality of any other principle.