The Daily Grind: What still doesn't make sense to you?

We've got a pretty complicated hobby here, even by the frequently vexing standards of general gaming enthusiasts. There are more than a few elements that we have to wrap our heads around in order to play effectively, much less be on the forward edge. So it's kind of inevitable that we each find our own breaking point for where we stop understanding why we need to do some things. The whole series of explanations eventually turns into an endless rant that looks similar to English but just doesn't make sense.

You might have read all of the math for the defense cap in City of Heroes or the diminishing returns mechanic in Star Trek Online, but you might not have understood the numbers being flung around. Or perhaps it's something even simpler, like the very concept of the soft cap for Hit in World of Warcraft. Not for lack of trying, your brain just won't process it. So what still doesn't make sense to you despite your best efforts? Is it a small aspect of gameplay or something you urgently feel the need to get right? Has it made a major impact on your playstyle?