I wonder if Brian Kerninghan was using modern tooling or that comment was using quote from 70’s.
I can debug .NET application and change code live, change variable states if needed. Watch variables and all kinds of helpers like stack navigation was immensely improved since I started 15 years ago.
I can say debugging Java/.NET applications is totally different experience than using debugger from 1999.
Multi threaded apps debugging and all kinds of helpers i visual debuggers.
I just fail to see why someone would waste time putting in debug statements when they can configure debug session with conditional break points.