People who feel like they are doing great work and motivated to do great work.
Yes, this is (verifiably) true. One must be aware, however, that positive feedback is usually going to be ineffective, thanks to natural "regression to the mean" effects, elucidated wonderfully in this Veritasium video[1].
(The point, in the end though, is that performance is going to statistically improve if people do worse than average, and do worse if they do really well, regardless of the feedback you give them", which is called "regression to the mean". The net effect is that you might get a false positive for negative feedback, and a false negative for positive feedback if you don't account for the natural tension that brings everything back to average.)
One of the best ways I've ever seen is simply asking the right questions (What did they think of the <recent event>? How could it have been handled better? How could it have been prevented?) People get very defensive and find excuses if you tell them they fucked up, but if they can admit it themselves they tend to correct their own behavior.