Like innocence, for example. It's too late only when you realised you had lost it. How to, pray tell, retrieve such a state of mind?
Unlike innocence, though, what we're talking about is neither as valuable nor valued.
Indeed, we're talking about the ability to 'mug'.
Somehow, after National Service, there's this understanding that there is more to life than studying. The world, with its vibrancy and vitality, beckons. Why study for nothing more than paper qualifications? In this light, the motivation to study simply melts away. Every counterargument can't stand up to scrutiny.
My historical self - sounds cool, doesn't it? - would be horrified by the way I'm behaving now. If the secondary school/junior college XY were to time travel to Nov 2010, he would simply die from shock that his future self is so lackadaisical about studying. Absolutely petrified. Shell-shocked.
As it is, this present self is amused by how his past self would react if he ever encountered this present him.