This! I learned more trigonometry in 2 weeks when I was tasked with a digital signal processing project than I did in years and years of (objective-less) schooling.

An important addendum to this is that the objective has to be closely tied to the work — the feedback loop for learning and then seeing some results from that learning has to be tight.

I think this may be why in school grades were not a good objective, for me anyway. They were just too distant a reward from the work.