Feeling the fruits of your actions right away! Like in the tribal evolution days, you could sense the meat of an animal you killed immediately!
Most brains value immediate gratification a lot more, like scrolling on short-form content all day long. But the delayed gratification is usually a lot bigger, and more significant pragmatically. However, if the gratification is of the same intensity, it’s not a bad idea to just do it now to free up one thought from the mind. There is a recency bias (Downplaying the past), however sometimes it's not even a bias but a reality, or reality can be chaotic.
The problem lies in… the other things, like how boring studying is… I think modern society just conditioned poor school slaves to treat exams seriously, and calling everything else a distraction, which is literally HELL if they internalize that belief! Boredom in study hell, other things guilt... Immediate gratification is not dead if you can see that's a trap! Fun is fine, guys! Chill! :)