I love the analogies.
Personally, it's very hard for me to pick just ONE lens. It depends on the situation.
A day at Disneyland, I want my young and skinny 40mm.
Studio portraits, and wedding candids, I want the 70-200 2.8 IS II all day (my "big, busty, and beautiful").
Casual shooting: the 24-70 II, plain but effective
Night time events, low light w/o flash, the 35 L (my late night mistress)
I am absolutely NOT advocating getting these, just wanted to continue the analogies post above

35L is the older prim capable secretary... time-tested, totally dependable, trustworthy, a bit long in the tooth...she's been with the firm for nearly 10 years.
135L is the reasonably priced call girl, technically perfect, does a lot of stuff the wife doesn't do (get your mind out off the gutter guys! I am talking optics here).
50L is the ex wife... was great one minute but shifted the next... PMS mood swings that ruined the marriage. We had to part.
85L is of course the trophy wife... doesn't cook or clean, pretty to look at, big chest that you paid for through the nose, turns heads, and great to show off at the corporate party.