Um ... yes ... well ... I do do the sums before taking off, and the results are usually pretty good, but every now and then the wind is, indeed, not what was forecast. And then I ... turn left a bit, or right a bit, until it works, pretty much as you say. And it works - I certainly don't bother with that "I'm half a mile to the left so I should alter course by 2.387 degrees to the right and then I'll be back on track in 123.87 seconds" mental arithmetic nonsense.
But how much is "a bit"? - somewhat like my mother's recipes ("put in some [ie an unspecified amount] so-and-so") it seems to come with experience (not that I've got very much, but enough for that).