I’ve been thinking some more about what I wrote last week about selling in Disney(DIS) stock.  The thrust of my reaction to the sharp decline was, and still is, mild bemusement that selling only emerged as the company reported weak results from ESPN.  It’s not that disappointing earnings should not generate selling.  It’s that the handwriting had been on the wall about ESPN–and in vividly hued bold print–for some time before DIS’s 2Q15 earnings report.

Why no stock weakness earlier?  This would have been my strong expectation. I’m not talking about the results somehow being leaked to outsiders by the company.  Rather, I’d have thought that the market would have put two and two together and acted weeks or months ago on publicly available information about the cable industry–like Nielson reporting of subscriber losses at ESPN.

My conclusion was that the sharp fall in DIS shares on its earnings report might be evidence that Wall Street just didn’t know there were problems at ESPN, despite what I consider clear signals of trouble being visible for a considerable time.

I still think it is generally true that the stock market is becoming less efficient–and more like I perceive the bond market to have been throughout my time as an investor.

I’m no longer sure that DIS is evidence for my thesis, though.  Here’s why:

The key to successful investing in growth stocks is being able to sell them at the right time, meaning exiting as the firm is going ex-growth and before the rest of the world realizes this.

To me, the key signal is the breakdown of the conceptual “elevator speech” explanation of what gives the company in question its extraordinary growth potential.  In my experience, if we’re waiting for the first disappointing earnings report, we’re almost always hanging on too long.

The presupposition here is that the potential upside from my exit point is (far) less than the downside from being a holder of the stock when the disappointing earnings are released.  This assumes, of course, that I can recognize the point at which all the possible future good news–and maybe more than that–is already factored into the stock price.

My approach didn’t work so well for me in the case of DIS, where I failed to anticipate the fabulous success the company has had in its non-Marvel, non-Pixar movie business.

There is a second approach to growth stocks.  It argues that a well-managed company normally has more earnings growth tricks up its sleeve than any outsider is able to understand.  Therefore, it’s always too risky to sell when the conceptual story begins to unravel.  Better to wait for actual proof to come in through bad earnings.  Yes, one might lose 10% by selling after the bad report.  But that’s better than exiting at 40% below the stock’s peak.

In fact, I took this second approach myself, early in my investing career.

The difference in my thinking from last week and now:  my first thought was that information is not circulating on Wall Street as fast as it used to; my second thought is that investors may have the same information as always but they’re just using it differently.

Practical implications?  …they may be substantial.  My conclusion is still to look for more evidence.  My tendency is going to be to hang onto growth stocks for a bit longer than I might otherwise, though, figuring that others are going to do the same thing.   So the cost of waiting to find out if there’s another growth spurt left in a maturing company may be lower than it has been in the past. And I may no longer be committing the cardinal investment sin of underestimating the information the other guy has.