There are two camps in investing: those that think there is a bubble and those that think everything always goes up. There both wrong. Bubbles are inherent with a new wave of technology; each one is different and has its own circumstances. You should not wait for anything because you anticipate one. You cannot time the market well; you should focus on finding companies that either are in the process of developing a moat or adding or transitioning business models, but have not done any of these things yet. You have to analytically figure this out. There is no way to outperform the index by investing in AAPL because you think they have a great brand; so does everyone else.

The camp that thinks everything goes up is right to criticize the people that think there is a bubble because memory sold off, or a company had bad earnings. Technically, no fundamentals have changed, but the broader capital cycle explains why earnings are unsustainable and artificial and will collapse, and demand is high for a new technology because firms do not want to miss out; the initial buzz always comes down, data center backlog is a myth. More on the capital cycle here

This is a long way of saying just buy the index.