Like him, I use a debugger rarely. Not because I'm opposed; they're great when they work. But it means I don't understand what my software is up to. Which for me is a sign of design and code quality issues. Or just ignorance. Both of which are solved by working to clean things up.
My code is often just a class or two plugged into a behemoth. I know exactly what my code is doing, but not exactly how it's being called by the platform, or what responses is it getting.
I agree a debugger can help you figure out mysteries. But when I find myself using one, I try to ask: how could I have avoided having a mystery in the first place. Common answers: better tests, cleaner code, better design.
I wouldn't be so keen to say that these help "avoid mysteries" in the first place. Many algorithms that have better time complexity and space complexity are often much harder to understand than writing algorithms that sacrifice those qualities, but can be understood at first glance. For example, is it easier to understand code that performs a lot of bit wise operations, which is probably better designed and more cleaner than a piece of code that performs operations with strings and object?