Rusbult‘s investment model:
Commitment is the key to a successful relationship.
There are many factors with contribute to commitment, and this includes high investment, high satisfaction (measured by profit levels) and less attractive alternatives.
In terms of investment they can come in many forms, including Intrinsic and extrinsic.
Commitment can lead to people staying in relationships where they are not happy. This is because they have made investments which they don’t want to see go to waste