For much of 2017 there were all sorts of different takes and calculations about the handful of mega cap and large cap tech stocks that were doing all the heavy lifting for the S&P500. Here's the latest one I've seen;
This is a late cycle phenomenon and is a sign of an unhealthy market. While I believe this is inarguable what is very arguable is when this will matter. There is essentially no predictive value, at least none that I know of to this. The market's leadership, its breadth, has been insanely narrow for months and yet the uptrend is alive and well.
Another one I have been hearing about for ages is record levels of margin debt. Here's a chart;
Margin debt on its face is an indicator of excess and clearly it is at an all-time high but the chart looks like it is more of coincident indicator. Figuring when it will turn for real would just be a guess.
In past blog posts I have discerned between things to be concerned about and things to act on. There are for more things to be concerned about than to act on. The MANIA names, or some other set of stocks with a clever moniker, could continue to lead the market very narrowly for many months or not, there is no way to know. If you are going to have some sort of exit strategy, make sure you base it on something that has a reasonable chance of indicating an actual turn in the market. These two don't do that.