One of the biggest problem is that, together with the mindset of getting rich overnight (as you also said), they don't have the knowledge to assess that certain "offers" are (far) too good to be true.
And this goes from getting into HYIP or so-called "cloud mining" to sending money to various "Elon Musk" (and so on) impersonations or hacked accounts in order to receive back double the amount (since money grows on the trees, you know...)
Like many of us use to say, if you can't hold for 5 years, don't hold for 5mins, and if you can't bear -28%, don't expect +28,000%.
Make sure to have a long term investment plan
This is a different topic. Actually two of them.
1. People who jump in without looking around into certain altcoin that promises to make them rich (and scam them, obviously).
2. People buying into Bitcoin at FOMO and panic selling at the first price drop. This second one is not scam, actually. And here a good plan and "invest only what you afford to lose" does help.
and while you invest and wait, you can trade actively on the side. Could be P2P or actual spot or futures/margin trading on the side to make little profits on the way up.
This is a risky advice and I am pretty much against it. Trading is not for everybody and can get people lose money very easy, by buying crap at FOMO, falling for pump and dump schemes, or by using unrealistic leverage and so on. This is not for beginners; by far.