How a team got this far this quick

Skill and luck, as you'd expect

Met or exceeded expectations
Adam LaRoche
Danny Espinosa
Ian Desmond
Ryan Zimmerman
Bryce Harper
Jayson Werth
Roger Bernadina
Kurt Suzuki
Tyler Moore
Chad Tracy
Wilson Ramos

Gio Gonzalez
Jordan Zimmermann
Edwin Jackson
Ross Detwiler
Stephen Strasburg
Craig Stammen
Ryan Mattheus
Sean Burnett
Mike Gonzalez
Tom Gorzelanny
John Lannan
Drew Storen

Met or exceeded expectations but not with a good enough season to really help team 
Steve Lombardozzi
Rick Ankiel

Fell short of expectations but didn't hurt team 
Mike Morse
Tyler Clippard

Fell short of expectations and hurt team 
Xavier Nady
Mark DeRosa
Jesus Flores
Chien-Ming Wang
Henry Rodriguez

The Nats didn't have to waste a lot of at bats or innings on guys that hurt the team with their performances.  That's a combination of good roster management and good luck.

It's good roster management because there weren't a lot of players on the team, that even if they met expectations, still weren't good enough players to win games. Instead there were players that were talented enough, that even if they failed to meet expectations, like Morse and Clippard, they were still helpful.  Think about past Nats teams. Everything not only had to "go right" but had to go better than expected for the team to be any good. This team was going to be a  better than.500 team in at least the outskirts of a playoff hunt from the start of the season, unless things went wrong. The foundation was strong.

Good luck for a few reasons. Some of the few players that weren't necessarily guaranteed to be good enough to win games if they met expectations, instead exceeded them and were helpful. Think Roger Bernadina, Kurt Suzuki, Craig Stammen, Chad Tracy. These guys needed to have their best years to be useful and they did. No one important absolutely tanked. It can happen and you can't predict it well. Look at the Red Sox. Youkilis, Ellsbury, Lester, Buchholz, and Beckett all were All-Star caliber players last year who drastically underperformed for one reason or another and hurt the team. On the flip side the Nats did get an unpredictably great year from Desmond and the good starters met expectations, while the ok ones exceeded them.

Plus while they were knee-capped offensively early with injuries, they had their full team for pretty much the whole last two months* and they had a great lack of injury year on the mound.

*I was going to say they ended up with a typical injury year but I know some people will flip over that so I'm going to try to quantify it in another post to see exactly where the Nats fall with offensive injuries.  My guess is "not as bad off as you think"

Saying luck was involved is not meant to denigrate the Nats' accomplishments. The Nats put themselves in a position where they could succeed, where luck can make the difference. That is all you can ask of a team. In the past the Nats didn't do this. In 2006 you might say the Nats had more good luck than bad. Yes Jose Guillen tanked hard but they caught Nick Johnson's healthy career year, Soriano's best offensive year, and Ryan Church's too when he could play. They got great limited pieces of hitting from Daryl Ward and Escobar. Pitching wise Livan would have a bad year, but everyone else was what you'd expect (including injury risk John Patterson missing most of the year). All in all that team, too had more guys meet or exceed expectations than fail to live up to them. The difference was that team had a ton of bad players on it. Getting lucky only mattered in keeping the team above 70 wins.

This year the Nats held up their end of the bargain, putting together a team capable of competing for a playoff spot, and when things went their way we were all rewarded for it.