Startup founders do not have diversification or a fallback, and it's humanly fair for them to be concerned when things are on a serious downtrend with tech stocks.
If you're certain something is going to go up in the long term, it makes sense to buy as much of it as you can. You must be certain, and you'd better be right about being certain.
A Buffett-favored aphorism: "Too much of a good thing is wonderful."
If your goal is substantially different performance from a market average, a concentrated position is the ticket. But, unless you're really good, the best you'll do, on average, is average, in which case you'd do better by buying an index.
Insurance companies are wonderful to own because you get access to their capital. They have tons of floating capital that's held in reserves, from premiums, until it needs to be paid out for claims.
GEICO was a perfect investment for a young Buffet because he exchanged cash (liquidity) for even more liquidity.
Older Buffett bought the company.