"It’s all water under the bridge."

This statement suggests that anything that happened in the past should be left in the past—no matter what terrible behaviour is expected to be washed away.

If you’re on the receiving end of this, you feel you should be the bigger person and let “bygones be bygones” —even if you’re still carrying around the scars from the gaslighter’s previous behaviour. 

There’s nothing gaslighters love more than to move on without taking any responsibility for past hurts.