Decision fatigue

Despite their popularity decision fatigue, ego depletion and finite willpower are all concepts without scientific backing and we shouldn't use them.
The idea is that we have a limited pool of willpower and as we make decisions throughout the day this resource is depleted resulting in worse and worse decisions. Famous billionaires who wear the same clothes such as Steve Jobs or Mark Zuckerberg are used as examples of good practice in fighting decision fatigue, the more likely explanation is that they simply save time by avoiding the decision.
It is true early studies were promising, but during later replication attempts no evidence for this effect was found.
Read this Wikipedia article for information about this effect. The criticism section at the end has an explanation on how this misconception uncovered during the replication attempts.
According to this article, it is only people who believe in decision fatigue who report these effects. Change in believe and mindset seems to be the only thing you need to avoid this effect. Therefore not only believing in this effect is incorrect, it is actually harmful.