When will the NASDAQ really crash?

The underlying logic behind the previous two points explaining why the NASDAQ has been rising: profits are pushing it up + the three perpetual motion machines (401k, buybacks, global funds) are supporting it.
But the US stock market doesn't only go up and never down. Over the past 50 years, it has experienced 7 major declines of over 20%.
So the key question is: how to tell when it's a normal new high, and when it's truly time to run?
Signal 1: Corporate earnings growth turns negative.
The core of US stocks' rise is profits increasing.
If in any quarter, the S&P 500's overall earnings growth shifts from positive to negative — not just a slowdown, but actual negative growth — then be alert.
Before the 2008 financial crisis, the S&P earnings growth rate dropped from +15% all the way down to -30%.
In 2020, during COVID, quarterly earnings growth plunged directly to -35%.
Before every major crash, profits first collapsed.
Signal 2: The Federal Reserve suddenly turns hawkish.
Interest rates are the gravity of the stock market.
The higher the rates, the less attractive stocks become (because you can earn interest just by saving in the bank).
In 2022, the US stock market fell 25% because the Fed raised interest rates from 0 to 5% within a year.
Signal 3: People around you who never trade stocks start recommending stocks.
This is the most crude but most accurate signal.
At the peak of the 1999 internet bubble, taxi drivers were recommending .com stocks.
At the peak of the GME bubble in 2021, barbers were talking about options.
Every time the market is at its craziest, there's one feature: completely uninformed investors start thinking they are geniuses.
Finally, let's revisit those who always shout "bubble."
From 2015 to now, the S&P has risen from 2,000 points to 7,500 points.
In these ten years, every year someone has been shouting bubble, and every year the result has been: it rose again.
It's not that it won't fall, but the judgment framework of "it's too high, so I won't buy" has never been correct.
Because your judgment is based on price, but price itself has no "high" or "low" — only whether it's expensive or cheap relative to profits.
As long as profits are still growing, today's "all-time high" is tomorrow's "floor price."
When the S&P was at 2,000 points in 2015 and people thought it was too high, how do they feel about that price now?
In 2026, the S&P at 7,500 points, you might think it's too high.
But three years later, looking back at 7,500, you'll probably feel the same way.