This is a very good question. Understand that not everyone is confident of themseleves and the skills they have. Such that they fear to express themselves through their skills and other ways in case they open up to teasing or ridicule.
Some other people are not certain of what skills they think that they have, in this circumstance I would suggest talking to a teacher or trusted person who will be able to give some guidance. In general, I would encourage you to always be helpful to those that are shy so that they can flourish in life.