You have to be solving for different requirements. If your original solution for a specific problem wasn't perfect (because of the nature of the problem, e.g. o

You have to be solving for different requirements. If your original solution for a specific problem wasn't perfect (because of the nature of the problem, e.g. optimization), then your previous ability to "solve" the problem doesn't reveal anything about your level of mastery. Or, to put it differently, progress needs to be measurable.