sea legs

the ability to keep your balance when walking on a moving ship and not feel ill It took me a while to get my sea legs, but I feel fine now.

The ability to adjust to a new situation or difficult conditions, as in She's only spoken in public a few times; she hasn't found her sea legs yet. This expression was first recorded in 1712 and then referred to, as it still does, the ability to walk steadily on board ship, especially in rough seas. By the late 1800s it was being transferred to other challenging situations.