Know your aircraft's systems. It can save a lot of panic, or maybe even save the day, if something goes wrong.
For example: you have an alternator failure. Will your engine quit once the battery runs dry? (Not on most aeroplanes, but it will on my Europa.)
You have a vacuum failure. Will the RMI/HSI still be usable? (Not during, or in the few minutes after, turning, but they should be usable at other times - at least that's the case on the Arrow which I used for my CPL, but I don't know about any other aircraft.)
Both real-life examples which have happened to me. If you don't understand your aircraft you can't know how serious a failure really is.
FFF
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