If your speculative investment moons then your portfolio has risen to 95-99% speculative investment. At least thats a consistent case in crypto or a super quick and awesome private equity exit, both of which have multiple thousands of percentage gains.

So the people following that kind of risk allocation advice might already be starting from that second state. Rebalancing is an option, but its lame when everything has such high correlations to each other. And rebalancing when? Anytime the speculative investment goes over 10% of the portfolio? After you let it ride and its price got stable for a few days? Waiting a year or more for lower tax treatment on the rebalancing sells?