Statements that involve the future are always linguistically vague. In your paradoxical sentence, "will regret" could be interpreted as either "know at that mo

Statements that involve the future are always linguistically vague. In your paradoxical sentence, "will regret" could be interpreted as either "know at that moment that they will regret" or "come to know after the fact that they regret it". The former is a paradox, but the latter isn't. As life advice, I think it works better when you consider it amortized over a collection of choices instead of a set of serial choices each of which it must be rigidly applied to: One should make a set of choices using a strategy that leads some of them to be likely to be regretful (but presumably without being able to predict ahead of time which ones will be).