Rational decisions are generally made by people who are able to determine the possibilities of an outcome, while irrational decisions are based almost entirely on emotion rather than experience. People who have the ability to make rational decisions may be able to do so because they can push past emotional response triggers.
Those who make rational decisions make them in part based on history and experience. Those who make irrational decisions generally make them based on emotions and availability bias. Availability bias, or availability heuristic, as it is also called, is the notion that a person's memories are given precedence over analysis or consideration when making a decision. When using availability bias, a person is likely to rely on recent memories of similar situations rather than an assessment of potential outcomes.