Rephrasing Munger, it boils down to your opportunity cost. I do think Berkshire will be a solid holding going forwrd with very low risk of permanent loss of capital. But it won't shoot the lights out; its size makes significant outperformance highly unlikely. I started buying Berkshire in my thirties and it has been a rock solid investment. But now there are possibly better alternatives like Fairfax. But you have to do your home work and be realistic about alternatives & your investing skills in identifying them.
For LT Berkshire owners it makes all the sense in the world to continue to hold Berkshire even if it underperforms the index over the long term from this point forward due to significant amount of accumulated deferred taxes. For newcomers, the math is much harder; there are better alternatives depending on your skill level.