on second thought

/ˌɒn sˈɛkənd θˈɔːt/

/ˌɑːn sˈɛkənd θˈɔːt/

on second thought

used to state that one has adopted a different opinion

have second thoughts

/hav sˈɛkənd θˈɔːts/

/hæv sˈɛkənd θˈɔːts/

to have second thoughts

to start doubting a decision and begin to wonder whether it is the right or best thing to do

Examples

1. You know, on second thought, maybe I’ll pass.

2. On second thought I'm not gonna encourage you to go burn stuff.

3. I said, on second thought, forget it.

4. On second thought, you guys sure you don't want to just breathe the deadly fumes all day?