To work really well, it also helps to understand level N+1 or N-2, respectively--either by implementing a higher level abstraction in a lower level environment, or by working on two levels at once (and thus needing to understand the level below the lower level).

For instance, you might be stuck with using C or Java and thus have to reinvent higher level abstractions through clever use of function pointers or design patterns or something--hence thinking at N+1, implementing at N, and being mindful of N-1 as you implement. Or you may be writing in Python but optimizing code bottlenecks in C, hence when writing Python (N) you have to understand the C (N-1), and when writing C (N-1) you have to understand the assembly (N-2).

So by induction, you need to learn N - 2, N - 3, ..., 2, ... 1? I wholeheartedly disagree. By that logic, why stop at transistors? Let's get down to the physics of how transistors work, or hey, atomic physics.

Ehhh... only partially. If you need to work well at level N-1, then yes, the inductive proof works. They only mentioned knowledge about a level lower than you're working at, though.

My bad, I read it wrong.

Actually in case of transistors, it is better to understand how they really work on physics level, because many abstract models of transistor do not make sense.

I said "a good conceptual understanding." Not a complete understanding.