John Junkunc was a railroad employee who had a habit of losing keys. He then designed and made a combination lock so he could avoid the problem of losing keys.
One of his early versions next to a quarter for scale:
These early Junkunc combination padlocks had gates that lined up directly with the shackle. If someone were to try decoding the combination like a modern lock by pulling the shackle while dialing, the 'wheels' would become deformed as well as the shackle.
Normally, this problem can be identified by a dial that binds and is very hard to turn at a certain point, but turns freely for the rest of the dial rotation. (Similar to a bent spindle on a safe lock).