" Mental exhaustion can stem from several factors, but the most common one is failing to get sufficient sleep. Even if you manage to get to bed at a decent time, you might toss and turn all night. That’ll rob your brain of the restful slumber it needs to prepare itself for the following day. "

― Damon Zahariades , Fast Focus: A Quick-Start Guide To Mastering Your Attention, Ignoring Distractions, And Getting More Done In Less Time!