You can spend the same coins twice, but you do not end up with 2x as many if you don't spend them at all. So you can end up with 1x worth of goods and 1x in you

You can spend the same coins twice, but you do not end up with 2x as many if you don't spend them at all. So you can end up with 1x worth of goods and 1x in your wallet like you never spent them but you can't end up with 2x in your wallet.