Learning curve. Weird things like that happen, and you make conscious efforts to avoid letting your opponent do things like that in future.
Models have wounds, sure, but it helps to think like chess sometimes, and assume your opponent can "one shot" your own model (Which they often can, in one activation, with multiple attacks and/or cheating fate). Put your models out there, take the hit, hit his back, that kind of thing.
Rushing models straight towards an objective or towards his line isnt always the most effective method of play. (Although rushing models straight towards objectives is good advice in general )