Willow is named for the tree known for bending in strong wind without breaking, and the name is traditionally associated with flexibility rather than rigid strength. It's often read as suggesting a graceful kind of resilience -- adaptability treated as a genuine strength, not a compromise or a lesser form of endurance.
Sluggishness in response is due to range, or insecurity, or bad organization. - Picatrix (Andalusia, ~1000.AD)