Choose wisely, indeed! What also has mattereed a lot-- at least for me-- is knowing myself in the sense of whether I feel like something is "risky" or "not risky."

I happen to be pretty cautious, so my opportunity cost often is the cost of NOT doing something new. Others are "variety seekers" and might jump from thing to thing, and their "cost" is being too scattered. Neither of these are "bad" things... but it's helpful to know on which side you're more likely to make your mistakes.