I have wasted sessions every now and then. Usually, it is when there's something I'm afraid to talk about and I lose the nerve to bring it up-- or when I'm just depressed and there is nothing either of us can really do to change that.

I've also has therapists in the past that either weren't the right match or were actually harmful, so I consider those sessions wasted. I do not believe that there are no wasted sessions. it reminda me of a saying:

It's not that everything happens for a reason. Things happen and then we find reasons for them.