I follow a very entertaining pony blog called My Little Po-Mo. If you haven't heard of it, it's basically Overanalysis Central. I bring it to your attention because of this recent Pony Thought of the Day.

Alderp Hoovestein, anyone?

... and one day she overturns Twilight's entire understanding of physics entirely by accident. Because she's a very silly pony.

Overthinking can be fun, yes.

It's been mentioned before, but there are officially four general interpretations of Derpy:

1: An regular pony with no particular hindrances who lives a life as exciting as any other townspony. Good with mail because she knows what she's doing.
2: A silly and kinda airheaded pony. Messes up now and then but isn't treated worse than anypony else. Good with mail because she's dedicated and hardworking, and covers her own mistakes as often as possible.
3: A space cadet whose brain operates on a completely different frequency. May be insane or a genius or both. Only Pinkie Pie can fathom what goes on behind the eyes that stare through dimensions. Drops letters along her route that ends up with the right ponies thanks to predictive brownian motion on a quantum level.
4: Functionally retarded, walks into objects, can't speak, drools. Other ponies pity her and make sure she doesn't hurt herself too much. Drops letters everywhere, ruining mail for everypony.

2 is pretty much canon according to The Last Roundup. 1 and 3 are also fairly common in fiction depending on how serious the work is. 4 is thankfully mostly phased out, at least on the sites I frequent.

I'm rather fond of 3, because I like ponies who are crazy-awesome in general. But it depends on the work itself.