Know is way too strong of a word here. You know a firing is good when it's a salesperson who's been with your company for 6 months and hasn't gotten a sale yet. Scott Forstall was with Apple for what, close to 15 years?, and worked his way up to a SVP position managing the company's most important product -- there's absolutely nothing about this firing that an outsider who only "follows" Apple can confidently say that it was good. If it took Tim Cook this long to decide that the costs of keeping him outweighed the benefits, it definitely wasn't an easy decision and the repercussions are big unknowns.

Even us smarties don't "know" anything. Apple has been doing fine in the past with these execs. If there is discord, it's not affecting sales. Record revenue, record profit.

In the future there is now some uncertainty: was Scott Forstall the key to iOS? Is Jony Ive a good UI designer? Will Bob Mansfield retire again next year? If you don't like that uncertainty, it's a good time to sell.

I'm going to have to partially disagree with this.

I agree there is definitely information asymmetry going on. However, usually a movement in a stocks price is lead by institutional money. This is for the most part what every hedge fund competes on, a competitive advantage.

If you think that your observation has escaped institutional investors eyes then I'd disagree with you. I'm completely biased as I'm in the industry but I think most people would be very surprised by just how much the average hedge funder knows about the companies they have positions in.

There were rumors circulating a couple days before the announcement that this was coming.

I'm also in finance. I'm constantly amused by comments on HN that dismiss "Wall Street" and the investor class in general as being stupid when they show a poor understanding of markets themselves.

I don't play the market, but years ago, I got to watch a coworker of mine walk all over you guys with the Rambus stock. He made a ton of money and knew when to get out by actually understanding the industry.

Totally. Wall Street doesn't understand Apple like us HNers do.

EDIT: this was sarcasm.

And vice versa.