Our actions may be impeded by them, but there can be no impeding our intentions or our dispositions. Because we can accommodate and adapt. The mind adapts and converts to its own purposes the obstacle to our acting. The impediment to action advances action. What stands in the way becomes the way.
A subtle point hides in the first clause. Actions can be impeded — by traffic, by illness, by other people's resistance. Intentions cannot, because they are wholly in our power. The Stoic action is governed by intention, with the result held under hupexairesis, the reserve clause. So the obstacle that blocks the result does not block the action in the Stoic sense at all. It only blocks one form of it. There is always another form, immediately to hand.
Marcus Aurelius, Meditations 5.20 · trans. Gregory Hays (2002)
Context
The passage that gave Ryan Holiday the title and thesis for The Obstacle is the Way. Marcus Aurelius's claim in the Meditations is not that obstacles are good — it is that the Stoic conception of action absorbs the obstacle. The blocked road becomes the road, because moving toward virtue is what one is actually doing.