It’s essential to express feelings of dissatisfaction. If you suppress them in pursuit of “maintaining a positive attitude,” your positivity certainly won’t be sustained. Those feelings will only build pressure.
In your discontented expression, however, you’ll want to differentiate: are you complaining or are you venting?
Consider, are you seeking to accomplish a goal?
Complaining often amounts to making small talk with a colleague or friend about an external circumstance. You don’t have any intention to productively change the circumstance, you just want to “bond” over small tragedies. Complaining is an unconscious, habitual exercise in negativity bias. You rarely think actively, “now I would like to complain about things outside my control because I think it will benefit me.” Complaining begets more complaining.
Venting is less about the external circumstance, and more about your authentic feelings in regards to that externality. It allows you to gain perspective. A friend or colleague can meet your needs for visibility, empathy, to be heard, to be understood. It can be an effective tool to reset your emotional base.
Ultimately the difference is, are you clearing out the cobwebs or generating more?