The numbers tell a striking story about where this year's market gains are really coming from. Two names—Alphabet and Nvidia—account for roughly one-third of the S&P 500's entire climb in 2025. That's a pretty concentrated rally.

What does this mean? Big Tech isn't just participating in the bull run; it's practically carrying it on its back. When such a small slice of the index drives such outsized returns, it raises questions about breadth, sustainability, and whether we're looking at genuine market strength or just a handful of heavyweight champions propping up the scoreboard.

For those tracking capital flows and portfolio diversification, this concentration is worth keeping an eye on.