To burn a bridge means to be entirely done with something. It's an affirmative act which cannot be reversed.
I've been guilty of not burning bridges that should have been burnt. It's painful to end relationships or situations that no longer work. It's easier to bob along aimlessly in a state of dysfunction than make a clean break.
When I did manage to finally light the match, it was because of a simple realization: eventually everything must come to an end. It wasn't easy to admit that something I put a lot of myself in was over, but at least I could stop spending time and energy trying to resuscitate it.
Also, with a bit of distance from the dysfunction I was able to ask myself questions. What was my part in why this didn't work? Why did I let myself feel trapped for as long as I did? What responsibilities did I fail to meet? Being on the other side gave me the space I needed to learn and grow from my mistakes.
You're not done with something until you choose to be done with it. Make the decision, light the match and see the light.
Choosing to be done with something wakes us up. We get back to making choices. We take steps on our own behalf. We replace dysfunction with acceptance and clarity.
That "best light" you get from a burning bridge, that's enlightenment. Are there bridges in your life just begging to be burnt? What is the light illuminating for you about letting go and moving on?