People in relationships have different experiences and outlooks on life, and this may stop them from having the same investment in a relationship as their partner. This is normal, but many people never really notice it until it affects them directly. A person may be completely committed to their relationship and expect the same in return, yet they are shocked to find out their partner is willing to walk away for a seemingly insignificant reason. This is because their partner has less investment, and they may also have tolerance issues.
Relationships, even those where there is a wide variance in commitment between partners, do work well when both partners recognize their differences. As long as a partner is caring and remains committed, the relationship can be successful for both people. A larger level of commitment may make a person dependent on their partner, but too little commitment may be a sign that a partner is ready to leave the relationship.