Clicker training is not a quick fix for problems. It is a carefully crafted language between horse and handler used during every interaction. People often have to let go of what they have always done in order to make room for a new way of interacting with their horse(s).
If frustration becomes part of the equation, for the horse or the handler or both, it is usually a sign of going too fast and expecting too much too soon.
The solution is usually to slow down, think things through, decide on the exact behavior required and write a careful shaping plan to achieve that behavior.
Keeping emotions (horse and person) on the calm/relaxed/joyful side of the emotional continuum is a major part of effective clicker training.