The thing that I always come back to, is to tell myself this:
"Just focus on what God has called you to do"
Because things can get out of focus so easily, and there are nearly always some people who don't agree with what you're doing. But what is most important is doing what God wants:
The world is passing away, and the lust of it; but he who does the will of God abides forever.
1 Jn 2:17
Jesus, in the Garden of Gethsemane, was faced with the sorrow and torture that he was going to have to endure, and submitted Himself to God's will.
"O My Father, if it is possible, let this cup pass from Me; nevertheless, not as I will, but as You will." Matt 26:39
So when I struggle with various things, I always try to remind myself just to concentrate on what God has called me to do and not to worry about what people think, how hard it is, or how unsuccessful it appears to be. And it always gives me so much peace just to focus on that one thing!