Answer:
Reasons
Often, we only observe a particular individual in certain situations, such as only at work or only at the gym.
After observing a behavior, people seem to be cognitively hardwired to make a dispositional inference before factoring in any situational influences.
People are not very accurate when it comes to evaluating their own judgments.
Not a Reason
Decisions based on insufficient or inaccurate consideration of situational factors rarely lead to bad outcomes.