> What do you mean not their fault? I've seen wrong parts delivered by suppliers, so yes responsibility of an engineer who puts together a circuit is definitely checking that the parts are correct.

Let's not move the goal posts, please. If you're going to use a hypothetical situation as an analogy, make sure it's actually analogous. Yes, an engineer who puts together a circuit has that responsibility, because they're an engineer. They went through the required training that makes them an engineer and not just an engineering student.

> I find it hard to believe that the lab tech said it could never be the parts, considering how those things are handled in student labs, small parts break all the time.

And therein lies the problem. You "find it hard to believe" that the lab tech could have been that unhelpful, just like the lab tech found it hard to believe that the student wasn't doing something wrong. Both you and the lab tech are behaving in a way that is inappropriate for a senior mentoring a junior.

In my experience mentoring others, the first assumption should not be that the person you're mentoring simply didn't do enough and that they should try to do better. Yes, that might end up being the case, but most of the time there's also something else that could have been done better. Maybe the documentation is not clear enough, maybe the process didn't help catch the mistake, maybe the expectations I set weren't clear enough, maybe I didn't communicate well enough.

"Go check your work again" is rarely helpful, even in the extremely rare cases where that's the only thing that needed to be done and no other improvements exist. If you're really convinced that they merely need to check their work again, guide them to it.

That's why they are junior and you are senior, because they need more guidance than you do. They will not develop the necessary insights and instincts without that guidance.

> I've seen the other side of the equation as well, when things don't work students often just throw their hands up and say "it doesn't work" without any of their own troubleshooting expecting the tutor/lab tech/professor to do the troubleshooting for them (quite literally, can you check that we wired everything correctly...)

And in turn, you're arguing that the mentor should merely throw their hands up and say "go check your work yourself". Again, even that can be said differently: "Can you explain what you have checked so far and how you've checked it?"

> Simply saying "it wasn't my fault because I had a wrong part" shouldn't just give you an A.

You are drawing a lot of your own conclusions from what hasn't been said. In this comment thread, you have repeatedly and consistently shown bias through your assumptions. Yes, what you're saying could have been the case, but I see no evidence of it and no reason to simply assume it without at least inquiring about it.