In my opinion, a plan that doesn't assume that there will be losses is gullible, when you think and even more negligent, a leader that plans with this in mind is a true strategist.
As far as i know, in story, any commander or military leadership that just thought they could trample the enemy without any losses cause much more death and loss, even the loss of entire campaigns. The Vietnam war is an example, for whatever stupid reason the American military commander thought that they could waltz on Vietnam and be done with it... i will admit i am not an expert of any level in that or any war so whatever i wrong feel free to correct.