Even if bitcoin's investment thesis is stronger today than it was 10-15 years ago, bitcoin still is not guaranteed to be profitable in the future, and every person still has to figure out his own level of balance in order to not reck himself in terms of overly investing into BTC, even if he might end up being correct about bitcoin price direction projection as being up.
This piece literally sums up the whole idea of investing wisely which is by investing an amount of money you can afford to lose. Investing with a sense of moderation. We need not put all eggs in one basket and by way of this in figuring out our respective level of balance to avoid reckage is by diversifying our investment to other physical assets within our reach that we know can be profitable in the long run.
I am not suggesting that there is any need to diversify into other assets besides bitcoin and cash, especially for newbies who might be in relatively early stages of building their bitcoin investment. It can take 5-10 years or more just to build up a bitcoin investment size (at least the amount that you had invested into bitcoin) to be equal to 1 year of your expenses. Just think about a person who might be investing 10% of his salary into bitcoin, it is going to take 10 years, to have the amount that he invested into bitcoin to be equal to the amount of his salary, and so then there might be another question about whether bitcoin is growing in value faster than his salary is growing, and surely some folks might be in years of their career in which their salary is growing and others might not be receiving significant increases in their salaries through the years.
My main point was not about diversification but instead about NOT overly assigning expectations of certainty in regards to either where bitcoin is going and/or how long it might take bitcoin to get to such point that you expect it to go. Diversification may or may not help with mitigating that kind of a risk, and frequently I recommend against new investors to be diluting their investment by getting distracted into nonsense ideas that they need to diversify when they are barely even able to figure out their cashflow and they might ONLY be investing $100 or less per week. The more immediate concerns would be for them to get their cashflow management skills into a good and strong place, and to spend time building their bitcoin investment without getting distracted into other nonsense - including getting diluted into believing that bitcoin is not a good enough investment, even if it is not guaranteed. There are no investments that are guaranteed, even such a great investment such as bitcoin that might be amongst the better of investments, and perhaps even one of the best places to put money.. just not necessarily investing with a mindset and such sloppy finances and/or cashflow management practices to be presuming that its upwards price performance is guaranteed.
Now this doesn't mean that bitcoin doesn't have a bright future ahead to do better but it's just a way to guard oneself against future uncertainties everything being equal.
I am not a fan of diversification as a way to deal with balancing out a bitcoin investment beyond bitcoin and cash. Sure, if you get to a point that your bitcoin is starting to add up to a year or even several years of your expenses, then there might be some need to diversify beyond just bitcoin and cash, such as properties, equities, commodities, bonds and/or even business or some various cash equivalents. (not referring to shitcoins. and surely anyone tempted to invest into shitcoin should be careful to limit such investments, trades and/or gambling in shitcoins to less than 10% the size of their bitcoin holdings, which also might be too much to even allow up to 10% of the bitcoin holdings (without cheating by continuing to add value when shitcoins are losing, hopefully?) to be put into shitcoins.