Diversification merely decreases variance, but does not change expected return.
Whether this is wise depends on how bad it would be to lose a lot of your money (which depends on stuff like how old you are, if you have kids, a stable job etc.).
Sometimes it's better not to have too many eggs in your basket so you can watch the eggs that you have closely enough (or avoid having to spend a disproportionate amount of time in a $100 "investment").
For sure it is a good default advice to follow, but it shouldn't always be the rule.
I agree, but the original poster clearly is not enjoying the variance. Clearly the variance is a huge concern to him.
If he's fretting this much over losing a bit under half the value, in purchasing power terms, then how would he feel if it fell to zero?
If he 'knew' that BTC is going to rise significantly, as many posters on here do, then sure he should stick with the one egg.
But he stated that he does not know the future price of BTC, which is critical here.
So diversifying, which decreases variance, is clearly the right strategy for him.