When life is hard, it's easy to complain about it. We all do it from time to time, and it's okay to do so — up to a certain point.
If we do it too much, we become unbearable to be around, and our complaints tend to become reality. We simply begin manifesting what we are complaining about.
That is, of course, a bad thing, but it doesn't mean we cannot complain at all. It's actually healthy to get the agony of life out of our system; we just have to do it in a constructive way.