may be in a part of your life you will meet people who underestimate you. Perhaps due to your age, you are younger. or maybe because you are still junior in the work place.
But do not worry and discouraged. do not be too concerned what other people say. Just relax and do your work properly. Do your best, work faster and be good, Thus there is no gap that can make people will underestimate you. Maybe you are younger in age, but act professionally and friendly so that people who underestimate you can see who you are. be careful with boastful, lest you be so proud though you’re better than them. Stay humble.
When you are slighted, accept it as a challenge to prove yourself. Generally speaking, everyone starts from zero and later climbs higher, higher and higher, so there is no need to feel down when people disregard you. Arise and stay optimist, that everything is starts from small to large. So when you underestimated consider it as a snap for you to advance another step forward.