Based on discussion page for Chained Ghoul, we still don't know what causes this to fail, and it doesn't seem to be related to Will (alone, anyway).
So here's a data point with very high Will and 3 etheric power:
Ice shards surround the ghoul, pushing in for 12 etheric damage.
The ghoul extends one hand and a chain of shadowy energy begins to form, only to dissolve under your superior will.
Someone with low Will could try just opposing it with etheric…
In the beginning, men were mortal.