On my change this spring I screwed up during negotiations.
They offered, I countered at +13k.
While they pondered that I did some more math and said to myself shit...that 13k isn't enough to cover my old health care bennies and the retirement kickback.
They came back at +10k over their original offer so 3k below my counter.
I declined, and said my original counter of +13k was also now void and I needed +18k.
Took them three days to get over that bombshell but they said yes.