I used to get really wound up about making mistakes - having to undo things made me feel like a bad knitter, but after I read some articles on mindful knitting and some articles by pro knitters who were talking about their latest mistake, I realised that no-one doesn't make mistakes and that it's part of knitting. I factor in time for the screw up, and am only a little frustrated when I have to frog (except from when I nearly finish a project and the whole thing isn't right, then I have to put it away for a little while before I can face it again!).
It's a good metaphor for life - you screw up sometimes along the way, or it doesn't work out how it was supposed to, part of the process is to figure out where you went wrong, fix it, and just get on with it. Life would be better if I could see it like that