This fear is intricately tied to self-esteem because, at its core, the character worries they aren't good enough for others or are incapable of satisfying them. Similar to LETTING PEOPLE DOWN, the character may be driven to perfectionism or actively avoid people and situations that carry high expectations.

Seeking frequent feedback and reassurance 
Comparing themselves to others
Not engaging in activities that would pit the character against someone else
Using self-deprecating humor to temper how others view them
Making excuses for failure in advance (setting the stage, in case things don't work out)
Deferring to others in collaborative situations 
Blaming themselves when they don't measure up
Bypassing opportunities that come with high expectations
Wilting in the presence of critical people
Accepting all criticism; difficulty differentiating constructive feedback from what's unnecessary
Gravitating toward low-expectation activities and people who don't ask for much
Difficulty taking compliments
Apologizing for insignificant things 
Engaging in unnecessary professional development or attempts at improvement
Closely monitoring the activities of rivals
Constantly trying to up their game
Disparaging others to boost themselves up