This is a term used to when going to bed with someone. To make hay means to copulate in bed with a significant other, often not only for sex but for sleep too.
To take advantage of a brief opportunity while it is still there. To not waste time.
The saying comes from farming communities. There would often be only a short time in which the hay would be ready to cut- reap too soon, and the hay would be too green. Reap too late, and you run the risk of rain ruining it all. Still very good advice.
I just got a good job for the summer- I don't know if I'll have one this fall, but I'll make hay while the sun shines and save up for the winter.
To take an opportunity to do something when the time and conditions are near perfect or available.
From agriculture, when farmers gather the long grass growth of summer to dry it to produce hay as winter feed for animals; The best time to cut and dry the hay is during sunny days.
A:"There's a sale at K-mart this week - You wanna see if the have something for your sister's birthday?"
B:" Sure - Might as well make hay while the sun shines, and get her something at cut price!"
The striver is an interesting phenomenon that is seen across college campuses. In essence, the striver is an over-achiever who comes from a working or middle class family. He may be an immigrant. He may have been a slacker in HS who was "born again" into an academic wunderkind. Or he may just be an over-achiever who is keeping at it.
The striver is willing to sacrifice his social life at the expense of Phi Beta Kappa and Summa Cum Laude. The striver is the guy who stays at the library long after you are gone. The striver is the guy who takes 30 credits/semester and considers anything below an A/4.0 failure. The striver doesn't work on campus, he is too busy finding ways to pad his resume instead of working retail or workstudy. The striver lets his grades pay his education by applying to ten scholarships a year.
The striver is a future Soros/Fullbright/Rhodes/Gates/Marshall/etc. fellow. The striver lives to study. For the striver, their fun comes from the rewards they expect to receive in return for their diligence. Be it Law School, B-School, academia, or politics. The striver seeks to find the American Dream through academic success.
Anthony was a striver. He transfered from a TTT to an IVY and graduated in 2 years. He studied his ass off and went to Penn Law. He got a Biglaw offer. But lost it all because of an unmoderated mesasgeboard.