Think better of it/of doing something
Definition 1 of 2
Pro Tip 1/3Decision Reversal
Use it when you're about to do something but change your mind to avoid a mistake. 
She almost texted her ex, but she thought better of it.
Pro Tip 2/3Second Thoughts
Highlights reconsideration after initially deciding to act. 
He was going to skip class, but thought better of it.
Pro Tip 3/3Hesitation Marker
It suggests doubt or hesitation before making a final decision. 
I almost ate the last cookie but thought better of it.