"I think you are right, use it or lose it."
This might be the single most valuable piece of advice to maintaining capability, both physical and mental.
Regarding the issue that some of you apparently believe that passive is just fine, I'm here to tell you that momentum investing like coach d does, if done right, can make you a medium winner--not the biggest winner, but also not the greatest risk-taker. Again, I have a friend who does this, who has done very, very well for the past 10 years. All told, his returns have equaled mine...and, he has had to work at it even harder (longer) than I have.
Also, regarding equities, I will say again that out of the FANG stocks, I might actually buy AMZN, if it were for the long term (20 yrs), MAYBE also NFLX, but NFLX is going to run into significant competition in content delivery, which is why the move is on among all those players to content generation.
IMO much will be dependent on management team strategies. I admit I don't know enough about them at the moment to make an informed decision one way or another.