The first couple of times I saw it mentioned I had to google it. FOMO - The fear of missing out.
I've had a little stash of liquid Steem that I play "trader" with going in and out of Steem on the rise and fall of the price.
I sold my Steem yesterday, and now I wonder... Will I get another chance to get back in or not?
:)
What a nice moment of fear I experienced.