A few tales from my student days...
One of the first times my instructor chops the power to simulate an engine failure:
Instructor: "Where are you going to land?"
Me (after looking around): "That long grass field over there."
Instructor: "The one with the high voltage power lines in it?"
Me: "Errr....."
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Another time, unbeknownst to either of us, the battery in the plane had been changed recently but not hooked up properly, so wasn't recharging. I preflight the plane, contact ground, then the tower, check that controls are free and correct, etc..
My instructor noticed something was wrong, but waited until I started my takeoff roll (on a long runway) to casually ask about the fuel gauges (or something else that required electrical power.) I look, see it's reading zero, and quickly decide to abort the takeoff.
The instructor had me taxi over to the tower so they could explain why we stopped talking to them.
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I became a little more observant by the time I started cross country training flights. I'd meticulously explained my planned route to my instructor in advance, which involved going near Travis AFB in Northern California.
I'm flying along on a lovely day and make a rather abrupt 30 degree turn to the right.
Instructor: "Why are you turning?"
Me: "Because we were on a collision course with that C5 up ahead."
Instructor: "Just checking."
(I think they saw it... We were in uncontrolled airspace.)