Decision fatigue can be just as exhausting as physical fatigue and sometimes worse.
Since I read about the study in Israel showing judges made better decisions earlier in the day, I've become more and more aware of how exhausting the act of choosing can be. I can feel it, if I spend too long shopping I start to loose focus the same way I can feel my muscles cramping if I spend too long standing.
With Costco, I no longer have to choose between five types of Almond Butter, no longer have to search five dates to find the newest milk - one choice. Shopping at Costco is mentally restful.