If you truly trust that God has a plan for you than you can neither complain nor grumble about your life. I think we can all learn from Joseph’s words in Genesis 50:19-20 “19 But Joseph said to them, “Do not be afraid, for am I in God’s place? 20 As for you, you meant evil against me, but God meant it for good in order to bring about this present result, to preserve many people alive” (NASB).
When complaining we put ourselves in God’s place thinking we know what is best for us and what is not best for us. Philippians 2:14 “Do all things without grumbling or disputing” (NASB). This goes for everything, not just some things. It is God’s plan not ours, so when you complain and grumble you complain and grumble against God Almighty. It is a hard lesson to learn but when we realize what Jesus has done for us and where our eternal home is, there is nothing to complain about!