Complaining never does any good. It reveals how self-absorbed we really are and it highlights the things we are most prone to be distracted by. The distractions are crucial: most often, in our discipleship, complaints reveal that we have lost our focus on following Jesus and God's mission.
When Jesus visited with Mary and Martha (Luke 10:38-42), he ran into a situation where Martha complained about Mary. They were in Martha's home and Martha was doing the hard work of hospitality, serving Jesus and getting everything ready for him. Mary, on the other hand, sat at Jesus' feet to listen and learn.
Martha's complaint was simple: "Tell her to help me!" But Jesus didn't acknowledge this complaint as legitimate. He used it as an opportunity to teach that complaining distracts us from God's mission.
Jesus' answer was to call Martha away from her busyness, away from her distraction (v. 40), to the simplicity of resting with him (vs. 41-42). In her complaining, she displayed worry and anger. There was only one thing she needed--to be with Jesus. Mary was already doing this, and Jesus commended her for it.
To reinforce this idea, the very next story in Luke is about Jesus teaching his disciples the "Lord's prayer" (Luke 11:1-4). In this prayer, Jesus taught simple dependence on God and focus on his kingdom mission.
We complain when we are distracted away from this mission, when we are overwhelmed with all the things we think we ought to do, and when others aren't doing what we think they should do. Let us stop complaining. Instead, let us seek the Lord in prayer, sit as his feet, and keep our focus on his mission.