Frustration comes at many times in many shapes and forms. It is said frustration is a form of anger, I can easily believe this.
For me, frustration comes from not starting at the beginning and not understanding why the result is not positive and often makes seemingly unrelated tasks have negative outcomes.
Horses are very forgiving. If they trust you genuinely made a mistake, they often will offer an opportunity for a correction, on your part that is. That is, of course, if frustration does not creep in instead of the light bulb turning on. (This is the seemingly unrelated tasks portion of the equation.)
Please give your horse the benefit of the doubt when it seems cooperation is at a premium. Chances are something was missed in the translation from your brain to his. If possible, take a deep breath, hold it for a few seconds; let the air out gently and slowly. Give your brain a moment to “reboot”.
Frustration is by-passed. Be in the moment and proceed positively.