Principle is ever my motto, not expediency.

Deciding by what works right now is efficient and gradually erases any shape you had. Each convenient exception is defensible on its own, and the sum of them is a person whose behaviour cannot be predicted, including by themselves. Settling something in advance saves you from negotiating it while under pressure, which is the moment you will negotiate it badly. The point of a principle is precisely that it costs something occasionally.

Name one rule you will not break, and say it plainly to yourself before you need it. Then keep it the first time it becomes inconvenient, which is the only time it counts.