There’s more than one way to skin a cat. People not using a debugger are not mindlessly adding prints, sort of a poor man’s debugger. Those people are figuring out the problem from a different perspective. In your case, one may trying to come up with a theory as to what could cause a deadlock and think of ways to cause it to always happen consistently. Before running anything, they would be trying to understand what could possibly go wrong. Then they test the theory. You can perhaps see that, if someone is always doing that, they can get quite good at it. They would also develop quite a good intuition on what to expect from the code base over time. Whereas, someone who just goes straight to a debugger may not develop such an intimate relationship with the code base.

It depends on individual’s strengths and weakness as well. Neither way is going to be better for everyone. Each person has to find out what works for them.