If those companies eventually backfilled value, then they weren't overvalued. Investors just, and correctly so, valued growth over immediate revenue. Of course

If those companies eventually backfilled value, then they weren't overvalued. Investors just, and correctly so, valued growth over immediate revenue. Of course, growth oriented companies fall flat on their face plenty of times, but for your Amazon's and Google's, with hindsight I don't think you can call them overvalued with the information we have now.