Bridging, blocking, babbling, asking unproductive questions; these are all examples of ways we express our fear on stage. If we look at the issue with a critical eye, we can see that a large part of our fear is fear of change.
Fear of change creates resistance, and this resistance presents itself in the forms mentioned above, among others. When we give into our fear and resist change, we are unlikely to create anything of value in our scenes. Acceptance (that old familiar, "Yes, and..." attitude) manifests story, scenes, and characters that move everything forward in a productive and cooperative manner. Fear grinds things to a halt, manifesting nothingness.
An extreme example of fear of change involves an improviser being faced with their own character's imminent death on stage (we've all been in that position ourselves.) An actor who gives into their fear of change will do everything in their power to avoid that death, causing the scene to lose any power it might otherwise have had.
"Fear of change creates resistance"
An improviser who gives into and accepts their character's death has a powerful effect on the story; will the audience be appalled, saddened, amused, or happy at the death of the character? If you've created a strong character and set a believable environment, you have the ability to pull the audience along with you and elicit whatever response you want. Don't let your fear take that power away from you.
Die, already.
Happy improvising!