just to be clear I don't think Lisa was wrong here.

Then I'm not sure why you have an issue with the way people are defending her? It's defensible because she didn't cross any lines. If she had yelled, thrown things, been verbally abusive, whatever to the trainees then people would not use "that's the real world" as a defense for her. It'd be "holy shit, that'd be a lawsuit or an HR issue" instead.

OP equated Lisa being anything less than nice and bubbly with her criticism to "rude" and it's a very unrealistic, and really selfish, way to view things. If you slack off, don't listen to your teacher - then yeah, your teacher will not be sunshine and rainbows. Why should they be? You gave them the reasons they need to be unhappy with you and call you out on it.

No one here is saying you gotta cuss people out until you shape out. What people are saying is that it's unrealistic to expect gentle coddling every time you mess up. At some point, everyone is going to hear, "You're doing it wrong and you gotta shape up" point blank without frills or embellishments.