Sure. If valuations continue to go up forever, at some point they're over valued. The point was that those predictions have been silly in retrospect. DHH had a

Sure. If valuations continue to go up forever, at some point they're over valued. The point was that those predictions have been silly in retrospect. DHH had a widely shared post where he said FB wasn't worth $33B+ and it could never be. He was clearly wrong (off by an order of magnitude). Eventually there will be some overvalued companies (WeWork before the valuation plummeted might be a good example). But given how many bear predictions have turned out to be really wrong, it's good to be skeptical of similar arguments going forward (they won't always been wrong, but some have been spectacularly wrong).