1
general::
Phrase(s): think twice (before doing something)
to consider carefully whether one should do something; to be cautious about doing something. • You should think twice before quitting your job. • That’s a serious decision, and you should certainly think twice.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. Reconsider something, weigh something carefully, as in I've got to think twice before spending that much on a car. [Late 1800s] 2. not think twice. Take no notice, not worry about, as in She didn't think twice about flying off to Europe with a day's notice. [Mid-1900s]
American Heritage Idioms