[darkmighty]

(standard disclaimers above generic advice that may or may not apply...) Trust your intuition, but not completely, when it comes to work and challenge. We are all lazy because we have very strong instincts to save energy and avoid risks -- that probably makes much sense in nature (where significant risks can mean death to natural causes or conflict). Even today, if you have life set at a boring job, there's not much to be gained, naively and from a naturalistic perspective, from constantly picking difficult topics to learn and stay out of your comfort zone. I think I can call it naive because of course cognitive flexibility and keeping learning may prove its worth if situations change and your safe occupation isn't so safe anymore. But in the end, as another person called, I think the primary motivator is some hunger, some desire to produce great things, to stay sharp/awesome, to beauty, that goes beyond pure individualistic safeguarding.

If you want to avoid mental atrophy, my advice is to find that hunger, find some sense of intense beauty, and pursue it even if it goes against your instincts sometimes.

(also as others noted: you need to be in a position where you can plausibly even find and satisfy this hunger; if your work and commute occupies all your time that's not going to happen of course)