Why did the Pandavas spend thirteen years in the wilderness? Or, to put it somewhat differently: why were the Pandavas banished for thirteen years? Why did they agree?
That's the question I have been working toward in the last few Jayaries. Thirteen years is a long time in a human being's life, even by the superhuman standards of the Pandavas and Kauravas. It's long enough that you're no longer a contender for power when you re-emerge. It takes an extraordinary person - A Mandela, a Gandhi - to retain power despite being sent away for such long periods.
The answer I am working out can be stated simply: if you want to follow the dharma, you have to be ready for long periods of exile while you rework your understanding of its principles. In other words, cultivation of the dharma takes a long time, especially when your earlier understanding has been shown to be flawed.
If you agree with my assessment, you will also find yourself agreeing with Yudhisthira's behaviour during the years of exile. Why was he talking to rishis instead of building an army? Why does he listen to so many stories: Nala and Damayanti, Agastya, stories of pilgrimages. Why didn't he renege on his promise to the victorious Kurus?
The answer is simple: Yudhisthira believed that he needed to absorb a new vision of dharma first and renew his quest for power only after doing so. Note that he isn't giving up the pursuit of power; he isn't turning into a rishi. He is a ruler, but he wants to be a dharmic ruler.
It's a knife edge he's walking on. We know that he succeeds after thirteen years but it's a success that kills everyone except a handful. That's why Yudhisthira has to go back to school again in the Shanti Parva.