Bog shaman nightblood question

Hi!

Someone please explain this to me “if life cost is not higher than the maximum you could spend”

And what if I use lifetap?

I am afraid of my build not working: https://pobb.in/BTeLyga5JVlm

Thank you

nightblood
Skills gain a Base Life Cost equal to 25% of Base Mana Cost
spells you cast yourself gain added physical damage equal to 80% of life cost, if life cost is not higher than the maximum you could spend