This mimics physical exercise. You lift heavy weight actively, and then you go rest, then you come back and the next (day/week/month) you can suddenly lift heav

This mimics physical exercise. You lift heavy weight actively, and then you go rest, then you come back and the next (day/week/month) you can suddenly lift heavier (assuming you're getting the right nutrition/rest and avoiding toxic substances) Similarly the brain muscles, you work them out actively, then you rest, some background magic is happening, and when you come back and revisit it, all of a sudden the problem can be easier. You can do something / solve something that all of a sudden you couldn't do previously. The eureka/a-ha moment is a little unique to intellectual work. It's hard to find something that gives a similar rush to cracking a hard problem. Brings back some fond memories solving USAMO/IMO problems.