The Old Complaint
Often when someone is complaining they’re talking about how they felt some other time, not now. They are describing a past event that made them feel frustrated or angry or hurt. Sometimes people can work themselves into re-experiencing that feeling through describing the past situation, even though they were in a different emotional state before they started complaining. Other times they don’t re-experience the old emotion, they are simply describing it like a storyteller.
One of the main reasons to stop complaining is to be more present with what’s happening in the current moment. There’s no benefit to letting unrelated negative emotions from past events affect how you perceive your world today.