> Do you need to be in grad school to achieve this?
No, but grad school is a fantastic place for it. Just because you can (partially) make up for a missed opportunity doesn't mean that missing it wasn't bad.
> Learning the skills involved in focusing on one area can then be applied to another area later on.
The fact that skills involved in one area can be applied to another doesn't mean you shouldn't be acquiring skills in many areas. In fact, it supports my point.
Yeah, it is, and it's a great way to add years onto a career move that is paying you subsistence wages.
You can attend other classes once you're a post-doc (unlucky) or a professor (better). Then, the university is paying you to be there, rather than someone else trying to find a salary for you in their limited grant funding.
I was referring to the skill of being able to focus. It's one I ended up learning the hard way.