It’s a metaphor. With enough oversight, a qualified engineer can get good results out of an underperforming (or extremely junior) engineer. With a junior engineer, you give the oversight to help them grow. With an underperforming engineer you hope they grow quickly or you eventually terminate their employment because it’s a poor time trade off.

The trade off with an LLM is different. It’s not actually a junior or underperforming engineer. It’s far faster at churning out code than even the best engineers. It can read code far faster. It writes tests more consistently than most engineers (in my experience). It is surprisingly good at catching edge cases. With a junior engineer, you drag down your own performance to improve theirs and you’re often trading off short term benefits vs long term. With an LLM, your net performance goes up because it’s augmenting you with its own strengths.

As an engineer, it will never reach senior level (though future models might). But as a tool, it can enable you to do more.