mood dip and trivial pleasure

I went to a university of engineering to deliver our system. Our users are multiplicity of industry, which are universities of engineering and technology, the institutes of research, entertainment industry, manufacturing industry and so on. I had worked in the entertainment industry over 5 years ever, so I know the needs or questions in the entertainment industry. However I can't understand in the engineering and technology. I've never fail to feel blue when I go to our customer of engineering because I can't answer the specific question the customer asks. When I am asked the question I can't answer soon, I say to the customer, "I will answer it after I will ask it to the developer of this system." That is not desirable. I don't know myself why I work for this kind of job. I graduated from law faculty of a university. The job I work for now is out of relation to the specialty. Anyway, I emailed to the developer about this question. This question is difficult for me to understand, even more to explain in English. I honestly wrote to him if I can properly explain the question.
Next day, as I checked email I found the email from the developer. A little pleasure was in the email. He wrote that, "This is a very good question. I understand what you are asking." I was glad to read this even though this question is not my question. I just emailed. But this email encouraged me since I was depressed. I will keep working with skepticism if I am an adequate person for the job? For now, I will do my best.