My opinion:
I believe that a cover letter is not the best place to be overly confident. A person who is very confident on a cover letter might give the employer a wrong idea about himself. It could show that the person thinks too much of himself and is therefore not open to criticism or advice. It could also convey that the person likes success too much, and is therefore not willing to try something new and fail at it. Therefore, I think it is good to mention your accomplishments, but it is important to do so in a humble way.
Reply paragraph:
I disagree with the previous opinion. I believe that showing confidence is the most important quality that you need to project when writing a cover letter. In a cover letter, you are supposed to talk about your accomplishments, your qualities, and the thing that you can do for the company you want to work for. In order to ensure that you stand out, you need to make sure you explain these qualities fully, even if these could potentially sound like bragging.
