on second thought

1. Resulting from a revised opinion or change of mind, as in I thought I'd go to the movies, but on second thought I'd rather stay home. Similarly, have second thoughts means “change one's mind,” as in I've had second thoughts about moving to Florida. This idiom alludes to ideas that come later. [Mid-1600s]

Example Sentences

Then: “On second thought, I changed my mind.”

From Los Angeles Times

Or, on second thought, maybe it wouldn’t be a surprise.

From Los Angeles Times

On second thought, however, it’s more complicated than that.

From Los Angeles Times

On second thought, no: that would be like trying to count every pine needle in Yosemite.

From Los Angeles Times

But only two hours after this promise, Linn says the landlord texted to say: "On second thought, I want you to move out."

From BBC