It is interesting looking at a long term chart how obvious that it was due for correction. Having said that, it's easy to say that after the correction because 'the top' is impossible to predict.

But if investors hadn't been taking profits on the incline, then I have little sympathy for them skiing down the decline.

(This is a harsh opinion, but people getting into investing should be doing it actively, not passively, ie. do some research, make a plan. Also, for those who are invested passively, long term, via ETFs, then they're still up 55% as @Nition says, so they're all good)