eli5: Why do we always get strong urge to be lazy if its better for the brain to be active

Question

I mean its so much better for the brain to be active working doing useful things stimulating your brain or working out, we all have a reward system and everytime we finish a task we feel a sense of accomplishment but everytime you should be doing something that you know will feel good in the end you just get this urge of doing nothing today and just relaxing,
shouldnt our brain be chasing this sense of accomplishment? Where does this feeling come from

In: 7156

Answer 1

Our brains are not suited for the environment we have created, because our technology made our situation change faster than evolution goes.

The reason for a lot of behavior that is bad for you is that it used to be good for you, or even if it was bad in too much quantity, we’d have another negative reinforcement to force a different action.

So before we had agriculture and civilization at all, we had to hunt animals for meat and gather plants for vegetables. When you don’t know when your next meal is coming, carbohydrates that can be burned now for energy or stored later as a fat for later conversion into energy when you don’t have food, are very good to have when you can get them. So over the course of our evolution, our taste buds evolved to give us hits of dopamine when we tasted carbohydrates, and thus why people like sweet things, generally speaking.

Similarly: too much activity can be dangerous to us. Run too long and you can trip and break something, or just fall and die, and even if none of that happens, you’re using some of that energy that you’re going to need later.

But, importantly: we didn’t have a stockpile of food that we can easily replenish without finding it in the wild and picking it/killing it ourselves. So the good feeling of relaxing was eventually overwhelmed by the hunger pangs, but instead of a 10 meter journey to the kitchen, we had to run after a single deer for 14 hours until it collapsed.

Nowadays, we have to understand with our higher brain functions that there is a reward at the end of the unpleasant stuff, and that our brain won’t tell us we’re going to die if we don’t do it and so it’s worth the pain to get there. Which we can do, but it’s harder because it’s at a more complex level of cognition than our “animal” brain that has all that instinctive stuff like “hungry -> go get food”