We'll burn that bridge when we get to it (idea) by Lord Brawl

A fusion of two phrases:

"we'll cross that bridge when we come to it" -- we'll deal with problems as they arise. Not always a good policy - if your name is Hannibal and you're travelling with elephants, for example;
"burn your bridges behind you" - making irrevocable decisions. Retreating troops will burn the bridges behind them to slow up an advancing enemy. If you do this to advancing troops, you've committed them irrevocably to the assault. See burn one's bridges.

Thus when we say "we'll burn that bridge when we get to it" we acknowledge that we're going to make a snap decision, and live with the irrevocable consequences should we choose incorrectly.

Your last act as a free man should of course be to burn the scrap of paper	Burn one's bridges	You can't make an omelet without killing a few people	Farberisms
Hannibal	Any woman who thinks she is pro-life should ask herself	And then I crawled out from under the table	I love it when a plan comes together
SNAFU	Why is nasal mucus green?	No one knows my plan	such is the way for a survivor of broken promises
The chameleon effect	Only a simple computer program	The guy who may as well already be dead and therefore doesn't care about the consequences of his actions and is able to move with perfect freedom for the remainder of what will likely be a tragically short life	random acts of management
David Farber	heard at Wal-Mart	Random acts of kindness	ad hoc
High school can kill you	English As She Is Spoke: Idiotisms and Proverbs	snap decision