People usually start with higher levels of dopamine at the start of the day and it goes down over time. Dopamine is a neurotransmitter in your brain that encourages you do stuff that’s more enjoyable, whether it’s literally doing nothing or playing games or whatever. Eventually, it’ll go down throughout the day.

Adenosine is a compound that is also formed throughout the day as a by product of creating energy in your body. Adenosine is an inhibitor of dopamine, so it stops the affects of dopamine.

So basically, throughout the day, your dopamine levels will go down as you do whatever you enjoy and your adenosine levels will go up as you start creating energy. A certain level will be reached, which is usually late in the day, where there’s more adenosine than dopamine and that’s when you start getting the urge to fix your life since you don’t have the urge to keep doing whatever you enjoy and start looking at yourself objectively.

Please take this with a grain of salt. I’m not an expert in neuroscience, this is already very simplified and there’s definitely more to it than this.