Like to complain?

Do you have this kind of experience?
When you are relaxed or work something at your home, a phone rings. That is from your friend. S/he keeps talking about her/himself, mostly...complaints!
My day was "the unlucky day" today.

Actually, she is not even "my friend." Let's say, "an acquaintance."
But we have something to talk with. I got a call, but I couldn't take. I called her back from my cell phone(that is a point!), then...she kept talking for one hour!

Why did I listen to her? Because I knew lately she has been under the very hard situation in her private life. I wanted to say, "Honey, I have an important test on Sunday, and I have to work tomorrow. I have lots of household chores to do today, so I don't have time to listen to you!"
But I didn't want to be such a bitch to a girl who just got hurt.

However, I couldn't stop wondering.
Some people just want to complain all the time. They always seek "someone who is kind enough to listen to us without judging!"
I want to be a kind person, but I don't understand their feeling.
Why don't they know it's just waste of time? It's not only waste of "their" time, but also they are "eating" their victims precious time!

Of course sometimes I also need someone who just listens to me.
But, not ALL THE TIME! I can smell "such people," so I avoid these people as much as possible. However, as long as I communicate with many kinds of people, sometimes I just "can't get away."

...Oh! Am I complaining now!? I'm sorry!!!