cold feet, get
Also, have cold feet. Retreat from an undertaking; lose one's nerve. For example, I got cold feet when I learned the trip involves white-water rafting, or Don't count on including her-she's been known to have cold feet in the past. The origin of this term has been lost. In early 17th-century Italy it meant to be short of money, but that sense has never been used in English. [Late 1800s]