This is a "asking a question so I can answer it" question, hope no one minds.
As you may know, LaTeX provides two versions of most of its equation-like environments: One which updates the equation-numbering-counter and displays the equation number, and one which does not; for minor equations which you don't want to number. For example, this is the difference between
Since math.SE doesn't provide equation numbering, I habitually type the starred versions of these commands when using math.SE. This then causes all kinds of bugs, which frustrate me until I rewrite the equation in another manner. What should I do?
Here is a list of environments to which this question might be relevant (cribbed from Figure 5.1 in Gratzer's book):
equation, gather, multline, align, flalign, alignat
I only checked equation and multline.