The effect is of marginal value, really. Base focus is…unremarkable. Does make it hard to just binge learn stuff, which is ok, but I’ve never run out of focus before, and I’ve never seen the appeal of buffs to your focus. I guess it’s never been plausible, or necessary.
It needs some modifiers. Something like ADHD or something; double regen up to 100% but double the decrease. Or something of the like. Maybe something that makes it so that you lose it slowly on things, but it also goes up just as slowly. That’d make it more interesting.