I've been watching The Big Short during some of my morning workouts lately, and was struck by something. One of the characters is insisting that we're in a bubble, and his boss says something like, "You never recognize a bubble until after it's popped". The character insists there are always signs if you look.
That's a huge fallacy, largely because there are always signs everywhere of everything collapsing. I work in an FDA-regulated industry, and about 75% of the companies I know of are thisclose to getting a Warning Letter from the FDA the next time they have an inspection. However, you never know which one is actually going to get the hammer brought down and exactly when it's going to happen.
It's the same thing with the various investment markets. There are tons of signs of things that could trigger the next bear market, but you won't know exactly which one will push us over the edge until after it happens.
Not a terribly happy state, but it's the one we've been in for a long long time, and I don't see it changing.