User blog comment:Deshiba/Wit's End - rework/@comment-25996306-20160221211529/@comment-4022742-20160222104207

The Lifeline is a long lasting effect not something that kicks in from 30% down. It's named so you cant have both passives at the same time, which would be somewhat op. Your 40 dmg per AA is continual as well.

The Damage generated from this passive is supposed to be decreased with MR, so you generate shield slower against high MR players. Context here is that it's supposed to be used against squishy guys if you can reach them.

This is why people who Auto Attack a lot are going to like it. Anyone that gets a Devourer as jungler will probably want to get a Wit's end too.