cooperation

Shared suffering increases cooperation more than shared rewards do.

Groups that endure an unpleasant experience together develop stronger bonds than groups that experience a neutral activity together.

The research specifically compares painful experiences to non-painful (neutral) experiences rather than success-based experiences.

Cohesion is forged in the struggle, not the outcome.

Where this comes from

Study: Bastian et al., 2014, Personality and Social Psychology Bulletin
What the check found: Bastian et al. (2014) confirms that shared pain increases affiliation, but does not claim it is stronger than the bonding achieved through shared success.
Confidence: Solid, with limits

cooperationsocial trustbonding

One of these every day, and every one names the study it came from. When a finding is contested, it says so.