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Solitary is a passive skill in the Physicist skill tree which makes your shaman no longer have a soulmate on soulmate maps.

This can both be good and bad for your would-be soulmate, since some soulmate maps are either easier without a soulmate, or nearly impossible without one.
This will, in most cases, make it much easier as a shaman, though, since most of the time, your soulmate is more annoying than helpful.