Anyone can complain, but to paraphrase Aristotle, the trick is to complain to “the right person, at the right time, for the right purpose, and in the right way”, otherwise it’s just moaning, and nobody like a moaner (except other moaners, that is).
If you have a complaint it’s best to deal with it. Either you accept the situation as it is, or you don’t. If you are unable or unwilling to accept it, ask yourself who you need to speak to, and what outcome you want. From then on, it’s like anything else you want to achieve, plan it and go for it.
You also have to be super-clear about your own motives. We are moved to complain whenever we are unhappy, but we often fail to address what needs complaining about (out of fear, for example), and instead say that our unhappiness is due to something it isn’t. The problem that’s driving the complaint never gets a mention.
Complaints often go wrong because they are simply veiled attacks (disguised moans), because the complainer addresses the wrong person (who is powerless to help), or because the approach is wrong. For example, since people on the receiving end of complaints often see them as an attack, how can you reduce the likelihood of defensiveness so that you can get your point across?
Carrying around a complaint can be damaging to your wellbeing, and so can moaning.