Enough of the instant death moves

What is with these bosses that keep getting these instant death moves where you have to run next to the boss/attack to survive it?

If I've never seen an attack the natural instinct is to back off and see what it does. Dying to this crap feels like I've been cheated.

I'd be a lot more fine with this if it just did a lot of damage or of the attacks came out slower. It just seems like you have to react to the attacks before the safe circle even appears.