I would consider it like this.

People invest in ICOs as they are investing in some sort of business, but they keep FOMOing this is why it's working well.

Thing is that even if it's legit ICO there is no guarantee that it HAS to work. Soo... There is lot of room for scams and of course unintentional failures. Just keep up with the golden rule, don't put in more than you can afford to lose.