Don't lose hope in every mistakes it is the journey to forward in the success. Many people succeed in their life it is because of mistakes after that they work hard. They make a decision not to give up and try and try.
Yes, when we are having faith within our knowledge and strategies then we do not get disappointments on seeing any losses because we will be having confident to recover the losses and then multiply the capitals. Mistakes may happen at any time because even professional traders also may slip down sometimes as market fluctuations are not predictable all the times.
to me i think i personally never disappointed in trading. i am doing trad for a long time some time i earn money while some time i also face lost but i never disappointed in gambling. whenever i start using continuously, then i try to change my trading method. which at least prevent me from further lost and when i realize that now i can get my confidence back then i start trading in normal form, but i never get disappointed in trading while losing money.