The boulder is the obstacle at full weight — too big to lift, blocking the path or rolled uphill forever. Sisyphus's stone names the recurring task; the boulder blocking the road, the problem that must be gone around, split, or accepted.
Positive Resonance
The obstacle honestly weighed, the way around found
Shadow Aspect
The eternal uphill push, the path blocked by the unliftable
Nuances
Boulder on the path: the full-weight obstacle
Pushing uphill: the recurring futile task
Going around: the obstacle outflanked
The boulder split: the immovable divided into moveable