Truth and Stability
One of Yudhisthira's virtues - less endearing than his kindness, but still an important virtue - is his truth telling. Yudhisthira never lies. That's why his lie on the battlefield is devastating.
Or is it a lie? Depends on what we mean by truth.
To use a mathematical analogy, there are two orders of truth: discrete and continuous. Discrete truth is tied to language: is this statement you just uttered valid? Can it be backed by evidence? Can it verified by appropriate procedures?
Let's consider the dice game. Yudhisthira agrees to the terms of the sabha knowing full well that Sakuni is a much better gambler. Yudhisthira's dharma is a discrete dharma: having received a challenge, he will assent to its conditions independent of the consequences.
You see Yudhisthira's discrete thinking in his response to the losses during the dice game. "Do you stake your horses?" "Yes, I do." One down. "Do you stake your warriors?" "Yes, I do." One more down. It's almost as if his memory register resets after each throw and he can only respond to the circumstances of the next instance.
Discrete truth might be correct, but it's unstable. Every throw brings the Pandavas closer to ruin. What kind of truth is that?