have second thoughts

Meaning: If you're having second thoughts about something, you're having doubts about a decision you've made.

中文意思：怀疑，动摇，经过重新考虑而改变主意；（重新考虑后）改变主意。

For example:
1. You're not having second thoughts about moving to Australia to live, are you?

2. I've been having second thoughts about quitting my job. Maybe I should keep it for a while longer.

Quick Quiz:
Sid and Nancy were going to get married, and then Nancy had second thoughts so____.

a. they decided to wait

b. they're getting married sooner

c. they're getting a divorce