I think it basically means..
Say Dick + Kitt both got the same average from the players, it would be a tie. Dick gave himself 40% on the safety score and Kitt gave herself 20% on the safety score, whichever person gave themself the lowest safety score = safe.
So basically if you think that you might lose a question, give yourself a low safety score. If you think there is no chance you would get picked for a question, give yourself a high safety score.