Babies love putting things in their mouths: dirt, insects, bits of grass, their own poo. They have no sense of fear or self-preservation, and come up with endlessly creative ways to place themselves in mortal peril. Once they learn to talk, their constant experimentation with the world transcends the physical to the philosophical. They want to know everything. They are bottomless pits of curiosity, with very little in the way of attention span or self-discipline. Your typical two-year-old can only concentrate on a task for six minutes at a time. Young children are not self-aware enough to feel much in the way of shame, or embarrassment. Nothing is off-limits. In a word, very young people spend almost all of their time exploring.

The elderly are set in their ways. The only foreign objects they put in their mouths are dentures and hard caramels; occasionally followed by a fork to extricate said caramels from said dentures. They tend to have stable routines, rituals, hobbies, and social circles. They rarely try new things or experiment with new identities. They’ve lived long enough to know what they’re about, and they intend to wring out every ounce of enjoyment before the curtains come down. In a word, very old people spend almost all of their time exploiting.

The ‘explore-exploit’ constraint is one of the most useful ideas I’ve come across…