Trust is a key element of social relationships and a foundation for cooperation. It comes in as many varieties as there are links between people. In well-functioning relationships, individuals can trust that a parent or romantic partner will show them love, that business partners will hold up their end of a deal, and that a someone in a position of power will wield it responsibly.
To an extent, people also trust complete strangers — doctors, taxi drivers, first-time babysitters — to follow social rules and not to take advantage of them or their loved ones despite the opportunity. Society would fail to function in the absence of this baseline of trust.
The sense that one can depend on another person lays the groundwork for social exchanges yielding benefits like affection, a sense of security, and achievements that would be impossible alone. When trust is absent—or someone betrays the trust that has been invested in them—the possibility of a successful future relationship diminishes.
For some, building, or rebuilding, trust takes longer than it does for others. People higher on the personality trait of agreeableness, for example, tend to more readily indicate that they find other people trustworthy.