The concentration trade is getting extreme.

$SPY is now beating the equal-weight S&P by the widest margin we've seen in 24 years.

What does that tell you? A handful of mega-caps are carrying the entire index while the average stock is getting left behind.

This kind of divergence doesn't last forever. Either the laggards catch up, or the leaders roll over. History says both scenarios are messy.

If you're only tracking the headline index, you're missing what's actually happening under the hood.