Okay, so remember our third law? (You can’t break things if you don’t change them.) Well, that has a very important related rule, that every engineer on Earth knows, but sometimes forgets:
Never “fix” anything unless it’s a problem, and you have evidence showing that the problem really exists.
Of course, most of us know this as “If it ain’t broken, don’t fix it.” However, these wise words are frequently ignored, because many developers don’t have a good understanding of what “broken” means. Often, developers just imagine that users have a problem with something, and start fixing it. Or they go off and develop features that don’t solve anybody’s problem. This is far, far more common than you might think.
So that’s why I say you should have evidence that there’s a problem. Without that evidence, you could just be fixing things that aren’t actually problems, and if you go around fixing things that aren’t broken, you’re going to break things. And not only could you be generating bugs, but you’re wasting your time and adding complexity to your program for no reason. You need evidence that there’s a problem, before you start coming up with a solution.
What do I mean by “evidence”? Well, five users report that when they push the red button, your program explodes. Okay, that’s good enough for me! Or you push the red button, and you notice that the program explodes.
However, just because a user reports something doesn’t mean it’s a problem. Sometimes a user just didn’t realize that your program had some feature already, and so asked you to implement something else silly. For example, you write a program that sorts a list of words alphabetically, and a user asks you to add a feature that sorts a list of letters alphabetically. Your program already does that. (Actually, it already does more than that. This is often the case, with this sort of confused request.) So in this case, the user thought there was a problem, but there wasn’t even really a problem, even though he could maybe present “evidence” that he couldn’t sort a list of letters. (He just didn’t realize that he should use the word-sorting feature.)
Note that if you get a lot of requests like the above, it probably means that users can’t easily figure out how to find what they need. There’s some complexity that needs to be reduced on your end.
Finally, sometimes a user will report that there’s a bug, but actually that’s the program behaving exactly as you intended it to. In this case, it’s a matter of “majority rules.” If a significant number of users think that the behavior is a bug, it’s a bug. If only a tiny minority (like one or two) think it’s a bug, it’s not a bug.
The most famous error in this area is what we call “premature optimization”. That is, some developers seem to like to “make things go fast”. But they do it before they know that it’s slow! This is like a charity sending food to rich people. “We just wanted to help people!” Right—illogical, isn’t it? They’re solving a problem that doesn’t exist.
The only parts of your program where you should be concerned about speed are the exact parts that you can show cause a real performance problem for the users. The rest of the code, the primary concern is simplicity, not “make things go fast”.
There are infinite ways of violating this rule, but the way to follow it is so simple: just get real evidence that the problem is valid before you fix it.