Over-promising is just one aspect of unreliability. Having a “can do” attitude is also important. If someone hears me shoot down ideas too often, it’s likely they will stop bringing new ideas to me. Also, as a teammate, I must not communicate annoyance or a sense of being “put out” when another teammate needs assistance. A great teammate is eager to help the team. Knowing when to say yes, no, and maybe while delivering is important for preserving a reliable reputation.