S: Each class can only do one thing, ever! Gotta do something else? Lets add more classes that all inherit from each other!
O: Heh, no one even remembers this one, like, ever.
L: Ya, thats how inheritance works! Right? Right...
I: Hey, I know how to create interfaces! Interface all the classes!
D: OK, just stick the DB connection into the constructer and we've got the D covered, yesssssh!
Really though, IMO SOLID is somewhat overblown in many cases. It is just a set of guidelines for good OO design not any kind of iron-clad rules.