Expressing disappointment and frustration all the time is showing everyone a mirror of your life.
Expressing disappointment and frustration in moderation demonstrates your balanced life.
It's ok to express the negative feelings you have experienced from a situation. Challenges happen to everyone, and sharing those circumstances verbally sometimes can make you feel better.
It's when those negative experiences keep happening that one should take a deeper look within. It could be that those feelings are not caused by an outside influence, but is a result of what's happening inside.