One of the most uncomfortable moments imaginable in any team occurs when you have to point out to a peer that he or she is performing below expectations or behaving inappropriately. This is awkward because most people feel like they are sticking their nose into someone else's business, or artificially elevating themselves above their supposed peer.
Unfortunately, if team members do not call each other out in such cases, it will make everyone feel less accountable, which in turn results in missed deadlines, mediocre results and poor team performance. The team leader is then burdened with being the sole source of discipline in the team, as there is no peer-to-peer accountability.
In some teams, when members have developed good rapport, they are then reluctant to hold one another accountable, because they fear their valuable personal relationships will be jeopardized. Ironically, this reluctance can and will damage those personal relationships, because the team members will begin to resent each other for not living up to expectations and for slipping from the team's performance standards.
However, members of great teams do hold one another accountable and this actually improves their relationships, because they develop respect for each other for adhering to the same high standards. When there is trust in a team, the members who are pushed to perform better will understand that it is being done for the common good, and not take it personally.
At the end of the day, peer pressure is by far the most efficient and effective means of maintaining high standards of performance. Individuals who fear letting down teammates they respect will naturally feel pressure to work hard and improve their performance.
This is why peer-to-peer accountability is a key component in enhancing team performance.