I’m not sure if I understand you- FOMO is just the fear of missing out on investing in a company that has a likelihood of making it big.
In the case of Magic Leap, VCs bought into the team’s background and expertise and banked on the likelihood of their success/impact if successful and decided to risk it. It doesn’t mean they were 100% sold- just that the risk/reward calculation they made was favourable.
Had they waited for Magic Leap to be a ways farther in their tech, (and had Magic Leap delivered), the price of entry to invest would be astronomical and the opportunity would have been ‘missed out’ on.