Which psychological findings have great practical implications, if they are indeed true?

Overjustification comes to mind, as an example.

On a related note: if it is true, does that suggest that, as far as we take the diminishing utility of money for granted, by using extrinsic rewards, we are reducing the number of extreme performers? (in so far as we can't keep giving exponential rewards, and money/tokens/what have you motivates in proportion to their utility) I have seen it argued, that if you are not doing well enough to be expecting a non-interrupted stream of extrinsic rewards, you probably shouldn't be doing that thing. Does that lose any validity in this context?

Still, it seems like whether it's true should have some implications.

A more certain finding seems to be the poor transfer of learning. It SEEMS like this SHOULD have implications for the education system.

What else would? (like, even if stereotype threat existed as a significant force, it seems far less clear to me how that finding could realistically impact any policies or our behaviors)