I'm not sure how or why I knew but saving for retirement was important to me, when 401(k) plans were introduced I knew I wanted that. The company I was working for didn’t have any kind of retirement plan, eventually I started advocating for a plan and put my job on the line, either they implemented a plan or I was leaving. It worked, they started a 401(k). Then when another business started courting me I made the same demand, only way I would work for them is if they put a retirement plan in place, and it worked again.
Regardless, my advice to my 20 year old self would be save more, party less!