Build backup plans before emotions become attached to needing them.

Backup plans made in calm are honest. Backup plans made once you desperately need them get shaped by hope and fear, and you will bend the analysis to make the option you want look better than it is. The time to think about the exit is before you are emotionally invested in a particular door.

For a commitment you have made, write down now what you would do if it did not work, and what signals would tell you it is not working. Keep it somewhere you can find it. Later, when your judgment is compromised, you will be glad an unclouded version of you left a note.