Great question! Everyone makes one roll per test. If you succeed, you proceed unharmed. If you fail, you still continue on but you gain a Mark. The only thing that stalls the progress of the survivors is if they all die.
I have seen people narrate this in cool ways. You could fail a roll and describe yourself facing the obstacle decisively and competently, but walk away Haunted by the memory of what you faced.
This procedure is clarified a bit in the updated version we're laying out now.