Humans are creatures of habit. The heuristics (or mental shortcuts) we use to guide our decisions are so consistent across large populations that, given certain circumstances, human behavior is relatively predictable.1
There are numerous models of heuristics, but what is implicitly baked into every one is the notion that people prefer to use as little mental energy as possible when making a choice. Thinking is work. Decisions fatigue us.2 This is especially true when it comes to shopping—when offered too many choices, people freak out.