For years, owning Apple stock felt almost unfair. Every earnings report seemed to deliver another reason to believe the company had discovered a cheat code for capitalism. The iPhone kept selling. Services kept growing. Cash piled up faster than most countries could count it. Every time critics claimed Apple had reached its peak, the company politely reminded Wall Street that it had another few hundred billion dollars' worth of ideas left. Now the conversation has changed. The question isn't whether Apple is a great company. I think that debate ended years ago. The real question investors should be asking today is much more interesting: can iPhone growth still meaningfully drive Apple's stock higher, or has the world's most successful smartphone become too mature to move the needle the way it once did? That's a far more difficult question than simply asking whether people like iPhones. They obviously do. Walk into any airport, coffee shop, corporate office, college ...