Think twice about something/about doing something
Definition 1 of 1
Pro Tip 1/3Decision Weight
The phrase implies the decision has significant consequences, so it warrants extra caution. 
You should think twice about quitting your job without having another lined up.
Pro Tip 2/3Doubt Hint
Using this phrase suggests there's doubt or hesitation, indicating it’s not an easy choice. 
She thought twice about moving abroad, considering all her family was here.
Pro Tip 3/3Persuasive Caution
It can be used to advise or warn someone else about possible risks in their decision. 
He told me to think twice about investing in such a risky venture.