Excerpt from this article:
In case you missed it, the initials ICYMI stand for the first five words of this sentence. In the event you have, indeed, missed it (ITEYH, I, MI has not taken off yet for some reason), it’s most likely because you’re not on the Internet much, particularly Twitter, where individuals and outlets deploy it every few seconds to bring links to the attention of others who may not have seen them.
…The cumulative effect is overwhelming for both producers of content and its consumers. Those who put out work, understandably, want to make sure it’s not lost on whatever site is hosting it, let alone in the social media blizzard of “must read” links, one-off jokes and other self-promotion. When the home page of a website refreshes every couple of hours (or minutes), there aren’t a lot of conspicuous ways to showcase older material except through the referrals of Twitter, Facebook and the like.
Yet it is this eternal retrievability of anything online that panics us. … “ICYMI makes staying connected feel like a constant game of catch-up, like finding things at a slower pace warrants some kind of disclaimer.”