There is no such thing as relative truth.

You mean belief, which causes major problems when conflated with truth.

Belief is useful for planning, but needs a separate static truth to have predictive value.

An actual unchanging truth is extremely beneficial for planning. But if you're planning with open eyes, you know that what you actually have are probabilities based on what you know when you make the plan, which I believe to be GP's point.

Anyway, there's no other definition of "truth" that isn't a mockery of the word as used. In practice you work with the closest you can get at the moment, but you don't redefine your terms down to match.

Relative truth is more dangerous for planning.

I don’t plan to exit my apartment through the window because I know there’s no relative truth of what will happen.

Quick relative truths are used because the alternative is getting burned alive.

The absolute truth in your statement is the threat of getting burned alive. You make the decision to escape based on that absolute truth and then you choose the route based on relative probabilities to survive. But you wouldn't even be trying to escape at all if not for the absolute truth that a fire will kill or severely harm you if you stay.