You run the Mac into the ground, you drive away professionals.
You drive away professionals, the fewer developers make apps for iOS (which uses the Mac).
The fewer developers make apps for iOS, the lower sales you have (in your cash cow products, no less)
The lower sales you have across the board, the more developers have even less reason to develop for your platform.
The more developers have even less reason to develop for your platform, you slip into a deep sales slump.
You slip into a deep sales slump, you start canceling peripheral products and services in the ecosystem to "refocus."
You start canceling peripheral products and services in your ecosystem, you reduce your lock-in.
You reduce your lock-in, the more customers you lose to competing platforms.
The more customers you lose to competing platforms, the more cash you bleed out.
The more cash you bleed out, the more desperate you get with ever more gimmicky features.
The more desperate you get with ever more gimmicky features, the more your consumer brand image is damaged.
The more your consumer brand image is damaged, you become the laughing stock of the industry (such as RIM, Yahoo, old Apple).
You become the laughing stock of the industry and it's game over, man. GAME FREAKING OVER.
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Apple isn't somehow different than any other company that has suffered a decline. Apple got lucky back in the 90s, plain and simple. Their phenomenal leader returned and it's a success story unlike we've ever seen. But they're not immune. I've seen many other companies wander down this path to irrelevancy after enormous success blinded them. It has happened before, and it will happen to most companies at some point. As far as tech companies go, Apple is pretty freaking old. It's surprising that they've survived this long. It's not too late to turn things around, but all I'm saying is that they're no longer heading in the right direction.
No professional ever said "Holy hell my computer isn't thin enough!" They say "Dammit this thing is too slow! And I've only got 30 minutes of battery life left. No no no!" You can't just keep going this long between updates to the Mac and expect Pros to stick around. We are always under pressure to make bigger and better projects at higher resolution than ever before and many of us regularly update our hardware. In just a few years we've gone from 18-22MP RAW photos being common to 50MP. We've gone from 1080p30 being common to 4K60 with HDR. We've gone from having to design non-responsive websites with one dimension to responsive websites with 4-6 breakpoint dimensions, which massively increases the working size of our design files. I understand part of it is Intel's problem, but part of it isn't—and I'm not just talking about restricting their specs by making it so thin. Apple has a successful chip design team making the various chips for iOS, tvOS and watchOS. They could solve the problem for the Mac if they put enough effort behind it. I hope they are.
+1. Very well considered.