We'll start with this from Michael Kitces.
I've never been much of a strict rebalancer so much as a derisker. We use the word ergodic (ergodicity) here to talk about the natural tendency or inertia of equities to go up. That applies to sectors and
Meb Faber has asked rhetorically on Twitter a couple of times whether or not it is a good idea to buy gold when it is at all time highs. He said it is not a good time, it is a great time and of course has data to back that up. I am not concerned with taking that input literally so much as to take it as a reminder that setbacks along the way notwithstanding, broad equities tend to go up, same with sectors and same with many stocks (not all stocks). This is a variation on the Lindy Effect.
My preference is to think about reducing risk. I start most individual stocks at 2-3% of the equity portion of the portfolio. Over the course of more than 20 years of managing client portfolios, there have been several instances where individual stocks went on absolute heaters and did so for an extended period. I don't have a hard and fast rule about what percentage weight I take some off the table instead it is more of a combination of things to consider. It doesn't get better than this is a good time to take a little off the table. Also it is pretty easy to look at a chart and see where something has gone parabolic. The context here is not that something negative has happened to the company, just whether or not it has grown too large in relation to the portfolio.
At what percentage weighting would an implosion be problematic? If Sandisk now made up 5% of your portfolio and it cut in half, would that be problematic for you? What if it was currently at 10%? We're not trying to pick a top or predict something bad happening, this is simply a matter of risk management. If giving up 500% points quickly because of some sort of calamity for the stock would be too much, that tells you to sell some. I wouldn't sell all of it unless there was something negative about the company prompting action, I would sell enough to get down to an acceptable risk level if something terrible happened.
This gets us to looking through to your exposure to various sectors and themes in ETFs and making decisions about what sort of weighting to have. For example, the S&P 500 has just under 8% in Nvidia and about 18% overall in semiconductors. For someone who is a real indexer, they are probably content to have that much exposure. But from there, how many portfolios own both the S&P 500 and QQQ?Nvidia is just over 8% of QQQ and semiconductors are closer to 30% of that index.
Copilot says there are at least 40-60 narrower ETFs that own Nvidia at more than a 5% weighting. One of the advisors I started subadvising for last year were quadrupling up on Nvidia exposure with the S&P 500, QQQ, SOXX and the actual stock. This would have been great for returns and terrible for risk management and the advisor didn't realize the duplication he had.
If you want to build that way by all means, make an informed decision and go for it but the point is more often than not, people do not realize the extent to which they are loading up on the same risk. That won't be a problem until it is a problem.
Do you have emerging market equity exposure? Have you looked at what is going on with the holdings? Chances are the fund you use is heavy in Taiwan Semiconductor, Samsung and SK Hynix. So that is another avenue to the same sort of risk/theme. If you've looked through to your holdings and know what your exposure adds up to and you're comfortable with that weighting then you're all set.
The top five in EEM add up to about 30% of the fund, tech more broadly is just shy of 37%. It is important to understand these exposures not to avoid being overweight the sector or the AI theme but to avoid being unintentionally overweight.
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