go off at half-cock go off at half-cock /ˈɡoʊ ˈɔf æt ˈhælfˌkɒk/

verb

1. Act prematurely or without reflection or too soon  ( go off at half-cock , go off half-cocked )
   act prematurely or without reflection or too soon
    She wanted to quit her job but her mother told her not to go off half-cocked
   she wanted to quit her job but her mother told her not to go off half-cocked