Thanks. I'll try to answer your question as best as I can:
The biggest reason why I concentrate in insurance is probably because it's where I feel like I know the most how to evaluate a business. I know it's dangerous because this industry is inherently more complex than, say, manufacturing or retail, but for some reason I feel more comfortable there.
Berkshire is a significant part of my portfolio, so I feel like it provides me with some non-insurance diversification, and the insurance that they do have is extremely high-quality and backed up by a very solid balance sheet, so it makes me feel less nervous than if I had only insurance companies with less solid foundations.
Another reason why I've been concentrating on insurance is that, because of float, it gives me some leverage (more than 1 dollar working for every dollar I put in) without me having to do it myself (I don't feel qualified to do so).
I also like insurance right now because many excellent companies seem to be trading fairly cheaply historically. Not as cheaply as in 2008, but still pretty decent prices, good enough for me. I have a long time horizon, so I don't mind holding a bunch of insurance for a while even if it takes a few years for a hard market to come. I'd love to be well positioned when that happens, though.
"Invert, always invert."
So why shouldn't I concentrate on insurance? Hmm.
Maybe all the non-insurance stocks that BRK, FFH and MKL have in their portfolios don't give me as much market diversification as I think somehow. I'm not seeing it, but maybe that's something I'm missing.
It leaves me vulnerable to big cat events. But because of my long time horizon, if that happened it probably would just be a buying opportunity, as long as it doesn't cause so much damage that one of my firms goes bankrupt. Or am I too optimistic here?
I know I have to question my choice of concentration, but I do still feel more comfortable with insurance even knowing all this. I figure if it's good enough for Buffett, it should do fine for me, as long as I stay with high-quality corps.