Several months ago I was convinced God wanted me to quit my old job and take a different one, but it hasn’t worked out. In fact, I just got fired from my new one. Where did I go wrong? Or did God change His mind?
How do you know that’s God’s will that He want you to quit your old job? 
One possibility is that you misunderstood God’s will—that is, you thought He was leading you to do something, but in reality He wasn’t. Sometimes we confuse our own desires for God’s will, and instead of prayerfully waiting for Him to guide us, we run ahead and end up missing His way. Peter thought it must have been God’s will for him to attack the guards who came to arrest Jesus—but he was wrong, and Jesus rebuked him (see Matthew 26:50-54).
But you weren’t necessarily wrong; perhaps God has been leading you all along—confusing as that may seem to you right now. Listen: God is sovereign, and He has not abandoned you! He knows what you’re facing, and He can be trusted to lead you in the future. Don’t be discouraged; God will be with you in the future just as He has been in the past.
Sometimes I feel it’s very difficult to know whether it was God’s will or not. But one day we will see God’s guidance and understand it. The more important thing is to believe God’s love and good will for you, always believe, and ask Him to help you learn from this experience, ask Him to help you trust your life and your future into Christ’s hands. Remember: God often uses life’s hard times to make us stronger. The Bible says, “We know that suffering produces perseverance; perseverance, character; and character, hope” (Romans 5:3-4).