Only a few of my sessions were disappointing. In one case it was all her fault. Only saw her once. Another time It was mostly my fault. Poor communication from me and running late.
The other 2x it took missteps by each of us to make a disappointing outcome. Sometimes a good mistress and a good sub can't pull off a good session.
I can't begin to count the number of sessions I've had. Most were good to great.