To use a different analogy, take the "predicted automobile deaths." Yes, we know some people are going to die on the streets and highways, but we take all possible precautions from a public safety perspective to keep that number down.
And I learned in safety engineering training, that 99% of actions are the result of someone breaking a rule, whether intentionally or on purpose.
When you head into a battle zone, you are CONSCIOUSLY going somewhere where the risk of loss of life is high. And you try to assess that threat as much as possible. And when bad stuff happens, it is investigated thoroughly in order to figure out how it could have been prevented, with a possibility of avoiding mistakes, IF ANY, in the future.
But any way you look at it, casualties are NOT a "good sign." They are just a hazard we have to decide to live with.
The key point, though, is that you can't achieve your objective without engaging the enemy and that's almost impossible to do without sustaining casualties, even though the US has gotten very, very good at minimizing our own.