For fear of something/of doing something
Definition 1 of 1
Pro Tip 1/3Emotional Weight
Conveys a sense of worry that something bad might happen. 
He doesn't ask questions for fear of seeming ignorant.
Pro Tip 2/3Avoiding Risks
Shows someone is not doing something to prevent an unwanted outcome. 
She avoids investing for fear of losing money.
Pro Tip 3/3Cultural Sensitivity
The phrase may relate to personal or cultural anxieties, discuss with sensitivity. 
They speak softly for fear of disturbing others' peace.