Comment by ab111111111

I think the Key phrase from that quotation is "thinking harder". A debugger gives you all of the programme's state as a kind of vast animation, so it's easy to start working with one thinking "Something's going wrong here, so I'll just step through the whole programmme and see when things start looking like they're going wrong". It's then easy to miss the problem due to the vast quantity of data you have to parse. Using print statements, in contrast, forces you to formulate simple hypotheses and then verify or falsify them, e.g. "I think this variable in this function is causing the problem" or "I think everything's fine with the execution up to this point". I.e. the very fact that a debugger works so well at giving you an insight into how the programmes state can itself be part of the problem: it can be overwhelming.