I saw Alvy Ray Smith give a talk in which he mentioned how when he was writing code, he had to just keep flipping the signs and coordinates around in the equations until the math worked out right.

That made me feel a lot better about having to do the same thing all the time too! Nothing ever works right (or runs fast) the first time, and you have to just keep fiddling with it until it does.

https://en.wikipedia.org/wiki/Alvy_Ray_Smith