easy:
1. Shit goes into S&P 500 (pump phase)
2. Shit goes to 0. Your 401(k) invested into S&P 500 takes a dive (dump phase)
3. Retail holding bags (full of shit) phase.
Case study: Tesla, with a P/E ratio in the hundreds along with declining sales and TAM, is a part of the S&P 500 and, consequently, of many people's 401(k)s.