You should gain this within your first few runs. The blood tree is generally the easiest and swingiest if you're having trouble. I highly recommend working on income and focusing on crit stats, especially once you've spent some of your heritage points in the blood tree.
It's worth noting that the final boss of each Act will take damage from ALL minions on the map regardless of their position, and if you place yourself in a room with a lot of traps when you start the round, that will help too.
Good luck!