Get/have cold feet
Definition 1 of 1
Pro Tip 1/3Expression of Fear
Used when someone is afraid to follow through with a decision or action. 
I wanted to try skydiving, but I got cold feet thinking about jumping out of a plane.
Pro Tip 2/3Informal Usage
Common in casual conversation, but less suitable for formal writing or speech. 
She was going to move to New York, but she got cold feet and stayed.
Pro Tip 3/3Major Decisions
Often associated with significant life changes or commitments. 
Tom had cold feet about buying the house, even after signing the contract.