It turns out that making decisions is tiring and wears us out, more so than other (similarly difficult) mental tasks. At this point, a large body of research shows that whenever we make many choices in a row, the quality of our decisions gets worse over time.

Decisions that are especially taxing are those that involve self-control. For example, when people fended off the temptation to eat M&M’s or freshly baked chocolate-chip cookies, they were then less able to resist other temptations later on.

Self-control tasks and decisions also require more glucose in the brain than other mental tasks. Low or hypoglycemic levels of glucose lead to impaired decision making, poor planning, and inflexible thinking. In contrast, simple psychomotor abilities, such as responding quickly to certain cues, seem relatively unaffected by glucose levels.

This pattern is in line with other things we know about impulsive behavior and typical self-control problems.

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