Grahame, Dodds and Buffett say are all negatory re diversification. They all agree, "Place big bets on Cos whose SP is undevalued and future potential has a great deal of upside!" (of course after completing sufficient DD!)
While SAN doesn't fit all their criteria, undervalued with great future upside has been enough for me!
As Buffett says, "10 years, not 10 minutes!"
As Traps concurs, 10 years out the Green Belt will be looking very "sweet!"
RUF