There's a reason investors have blindly trusted Wall Street's “buy the dips” mantra since 2009.

In fact… there are 2.3 trillion reasons.

That's because since 2009 U.S. companies spent more than $2.3 trillion buying back their own shares, according to a report by Aranca Investment Research Services.

All that buying acted as a floor for stocks and launched the major indices to new heights.

But now, after watching stocks fall off the “Wall of Worry” this year, instead of climbing it, investors who simply bought the dip without any strategy are praying new buyback programs will start lifting stocks.

Too bad for them (and too bad for the companies that wasted billions of dollars watching their shares fall back to Earth), all the upcoming share buyback announcements combined can't put Humpty Dumpty back together again.

That's because sentiment about global growth, about the market, and about the long-term value of buybacks has changed.

And let me tell you, when sentiment changes, everything changes…

Why Investors (Used to) Love Buybacks

For the most part, investors love buybacks – and the positive sentiment they create.

That's because in a benign market at least, corporate buying puts a floor under prices. And that engenders positive sentiment.

Here's how…

In a bull market, multibillion-dollar buyback programs push prices higher to attract more buyers and create upward momentum. At a minimum, investors believe if share prices slip after running up, corporate buying will come in at obvious “support” levels and create another safe floor.

Fundamentally, spending cash on or debt-financing buybacks is touted by management as “returning cash to shareholders” by reducing share count, which reduces the number of shares the company's earnings are divided across.

So, by reducing shares through buybacks, earnings per share can rise even if actual earnings are flat or falling. And that's a source of positive sentiment for those holding those stocks.