I think that usually when people say that 10% of the work take disproportionally longer than they expect, it's because they're measuring the wrong thing. If you

I think that usually when people say that 10% of the work take disproportionally longer than they expect, it's because they're measuring the wrong thing. If you find coding easy, then writing 90% of the code doesn't equate to 90% of the work. Polish is very hard, and in most cases it isn't 10% of the work, it's more likely something about half the work. After all, that's exactly what distinguishes your product and makes it worth using. Not sure if thinking about it that way makes it feel better, but at least for planning purposes, consider calling the polish phase 50% of the work.