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A phrase used to describe the finality of a decision made by someone.

Once someone has made a decision and can not back out of it.

Derives from the immature act of sticking one's thumb in a can and attempting to pull it back out.
Jim: Why don't you just leave her?
Ted: I can't mate, I've got my thumb in the can now.

Wish I'd have said no to that I've got my thumb in the can.
by JohnJoeTheGood May 13, 2019
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