For one to be able to hold for long, that person needs another means of income to enable him not to panic during the bear market.
Really? You think that's just what it is? How about the decision to do so? How about those less experienced people who are yet new to Bitcoin? They may have other sources of income, but because they have not really experienced how prices can be so volatile, they can sell out of pressure just for the fear of not totally losing their invested capital.
You must understand the context before doing that comment, see what they are talking about, they have talked about investing strategies in Bitcoin and they say about the bearish market, of course the subject already has knowledge in investing in Bitcoin. I will agree with you if the characteristics of the subject are a beginner who does not know the market and investment starts in Bitcoin, even though they have other sources of income they are not necessarily holding their bitcoin when they find a bloody market.
Other income is very important so as not to interfere with the ideals of long-term investment in Bitcoin.
Actually there is nothing wrong with saving all of our assets in the form of bitcoin,
I don't know if you read correctly what Sir JJG said above and where he said that "we cannot be 100% sure that what we see as a reliable source of income can be reliable in every scenario."
So since you already said you don't believe in carrying all your eggs in one basket, diversifying your investment or source of income is a wise thing to do.
Storing all assets in Bitcoin is a good decision (to be faster in a heart attack and higher stress) lol.
With a fluctuating market, it is certainly not a good option for financial health.