You know.. that's true. Very true. But I think it should come with a caveat... any random person you interact with could one day be a valuable ally, yes. But the odds of any given person blundering into your life in a significant position to aid (or harm) you, late down the road, by happenstance, is very low. This is my observation anyway.

I don't go out of my way to antagonize people, or burn bridges, but I also don't go out of my way to pander to people or kiss ass just to maintain a "bridge." And while you never know what you don't know, I have zero reason to believe that any relationship I've damaged through this attitude, has ever had any negative consequence subsequently in my life. The world really is a big place, and you meet a LOT of people over a lifetime... there's a steady stream of new relationships coming along, displacing the old ones.

Again, this isn't to say one should go out and wantonly burn bridges for no reason, and it's not to say that one never benefits from a happenstance encounter with someone from a different part of your life. But I do think we should question how important it really is to worry about burned bridges - especially if your intuition tells you that the person is question isn't likely to be a future ally anyway.