The Investment Model of Commitment: Why People Stay (and Why They Leave)

Satisfaction, alternatives, and investment — the three levers of lasting commitment

What determines commitment in a relationship?

Caryl Rusbult’s Investment Model proposes that commitment is driven by three factors: satisfaction (how good the relationship feels), quality of alternatives (how appealing life outside the relationship seems), and investment size (what you’ve put into it that would be lost on leaving). Commitment rises with satisfaction and investment, and falls as the alternatives look better — which is why the model explains the two cases a simple "are you happy?" account cannot: satisfied people who leave because something outside became more appealing, and dissatisfied people who stay because too much would be lost. Rusbult first tested it longitudinally in 1983, and she and her colleagues later built the Investment Model Scale (Rusbult, Martz & Agnew, 1998), which measures the three inputs separately, so you can see which one is actually carrying your commitment. All three are modifiable — and understanding which is weakest gives a precise target for strengthening commitment. The model has extensive empirical support across diverse relationship types and cultures, including a meta-analysis by Le & Agnew (2003). Its honest limit is that the evidence is correlational: the three factors reliably predict commitment, but the model describes what holds people rather than prescribing what should.

Most people think about relationship commitment as a feeling. Caryl Rusbult’s Investment Model reframes it as the output of three inputs — how good the relationship is, how good the alternatives look, and how much is already invested. Rusbult, a social psychologist who spent her career on interdependence in close relationships, developed the model out of exchange theory and first tested it longitudinally in 1983; it has since been applied well beyond romantic couples, to friendships, jobs, and even why people stay in relationships that are hurting them. This reframe is practically powerful: it tells you exactly what to work on when commitment is eroding, and it explains why satisfied people sometimes leave (high alternatives) and why dissatisfied people sometimes stay (high investment). The most useful thing it gives you is a diagnosis rather than a verdict — "should I stay?" is close to unanswerable, but "which of these three is currently holding me here, and is that the one I want holding me?" is a question you can actually work with. It is worth naming the shadow side up front: commitment sustained by investment alone, with satisfaction gone, is what the research literature describes as feeling trapped rather than committed, and the model is just as good at making that visible. Below are practices derived from each model component.