You can simply delay your "yak shaving with unknown problems" until too late. Your velocity with simple things will be fine just until few weeks (or days) befor

You can simply delay your "yak shaving with unknown problems" until too late. Your velocity with simple things will be fine just until few weeks (or days) before deadline. And then you're toast. ;) So you should take into account uncertainty and importance. First you should do all uncrtain and important things, then certain and important and, finally, certain and less important. And your velocity will vary greatly then, very slow at the beginning and fast at the end. It is almost meaningless, I say.