Within the past few weeks, Apple joined Nvidia as just the second company in history to eclipse a $5 trillion valuation. Milestones like this always spark the same debate: The market is too concentrated... a handful of companies are too dominant... trouble must be right around the corner. Maybe. But before reacting, it's worth asking two better questions: How much bigger can these companies actually get? And does the answer even matter for your retirement? In today's email, I'm tackling both...