The thing about complaining is that there is no resolution, only a thing to fight with. Fighting something, which is essentially resisting what is, has no benefit ever. what has already happened, has already happened and will not change ever, the past is gone. Even if it was only a second ago. Inner peace comes from accepting inside what has occurred, a thing that we cannot change.
What complaining allows is the mind to feed its ego and the pain body, which constantly needs a drama to survive. It allows a sense of importance, or a sense of being a victim or both to manifest, something to be indigent about, to centre things on ‘me’. ‘Me’ is what the ego loves.
Complaining is habitual and once your mind gets you hooked it spirals downwards until only a continual state of complaining will manifest.
When we accept without resistance, then it is a minor thing of a trivial nature that occurs, that has no impact on our state of wellbeing. When the mind complains, it is a major incident, that only leads to more major incidents and suffering.
Being in the moment ends the need to complain and removes the suffering it causes us and those that have to endure listening to it. It also leads to peace within.