Why do people stay in relationships that make them unhappy?
Because satisfaction is only one of several things determining whether someone stays, and the others often outweigh it.
The most useful framework here is Caryl Rusbult's investment model, which holds that commitment is predicted by three factors together:
Satisfaction — how good the relationship feels relative to expectations.
Quality of alternatives — how good the perceived options are, including being single. Someone who sees no viable alternative may stay in a relationship they find unsatisfying.
Investment size — everything that would be lost on leaving. Years, shared finances, a home, children, mutual friends, family relationships, a shared identity. Crucially, investments are non-recoverable, which is what gives them their hold.
The model has held up well across many studies, and it explains something satisfaction alone cannot: two people equally unhappy make different decisions depending on their alternatives and investments.
Other well-supported contributors:
Sunk cost reasoning. Having already spent years is not a rational reason to spend more, but people consistently weigh it as though it were.
Intermittent reinforcement. Relationships that alternate between good and bad periods can be harder to leave than consistently poor ones, because the good periods renew hope on an unpredictable schedule.
Practical constraints. Financial dependence, housing, immigration status, childcare and health insurance are real barriers, not excuses.
Fear and social pressure, including judgement from family or community.
Identity. After long enough, leaving means dismantling a picture of your own life.
Why naming this matters: "why don't they just leave" treats staying as irrational when it is usually a response to real constraints — a point that matters especially where control over money, housing or contact with others is part of the dynamic.
If you are in an abusive relationship, a domestic abuse helpline can help you plan safely.