As an illustrative example, the other day I had a soldier (Special Forces tryout) who was drunk out of his mind and having a severe PTSD episode. He had already demonstrated that he was a) feeling no pain and b) not present in reality, in his mind, due to his actions prior to police arrival. I was the only one onscene, waiting on backup, when he spotted me and started coming towards me.
I had no desire to do anything to hurt this man - it wasn't his fault that he was having his episode. However, if he was feeling no pain, my pain compliance techniques, OC spray and baton would be ineffective, and I carry no taser. He was smaller in height and weight, but in FAR better shape than me.
The Force Continuum is a vague guideline that comes down to two simple requirements: is the level of force reasonable and necessary?
In that situation, if he had decided to bullrush me, as he was beginning to do, there would have been very little I could have done to defend myself. I would have needed something to incapacitate his system, rather than cause him to comply via pain (i.e. taser, supersock, or lethal force). I only have one thing on my belt that would have fit the bill.
Doesn't mean it would have been an easy call to make.