Oh, I don't know about that.
Seriously. Mental energy is impacted by a lot of things. And I've had to come up the hard way, just due to my circumstances early on.
Doing this gets harder as we age. But under 30?
It's there for an awful lot of people who want it. There is one's own drive, and there are the kinds of friends one makes and how time is used.
For the longest time, I read one tech book a month. Just needed to gain perspective. I also turned the TV off.
The amount of time this frees up is AMAZING.
Networking pays too.
And for some people, that's starting a business. For others, it's self-employment / contract work. Still others, it's taking hobbies and spinning them into skills they love to exploit.
Lots of ways to get this done. And frankly, doing it consumes 10 to 20 percent of one's free time outside of a 40 - 50 hour work week.
That's not too much time. Just turning the TV off delivers that time for a very large number of people.
There is a clear cost for some jobs too. Where those work demands punch up above 50 hours, it really does start to get tough to do other things. Sadly, we've a lot of people stitching several basic jobs together and that eats a lot of their time.
But for many, who are just working full time, it's possible to make personal investments.
And what a lot of people don't get is the compounding that comes from doing that consistently.
One hour a day spent on this kind of thing compounds better than 5 hours on Saturday does. (though it's really nice to do both!)
Simple things, like just getting up early, make a big impact. Eating healthy, managing sleep to 6 hours instead of 8.5...
What is worth what?
Many people don't see a pay off they can visualize and believe they can actualize, so it's not worth it, and so they don't do it.
Setting aside difficult circumstances, it's often that simple.