Gene R. Cook of the Seventy said:
If you’re praying for something that really matters, you can count on the fact that the devil will get involved. He’s eager to do what he can to thwart you. He will do his best to dissuade you from going forward. He’ll give you such thoughts as “you can’t do it. You’re not worthy enough. Your family’s got too many problems. You can’t do what the Lord requires.” He’ll engineer whatever he can to try to make you doubt. So you may as well know up front that he is going to tempt you.
When you attract the devil’s attention and he starts to give you more opposition that you normally have, that’s a great sign that you’re on a course that pleases God and displeases Satan.
I’ve found that when you begin to pray for something that really matters, many times things get worse, not better. Often the cause is Satan and his helpers, who are doing their best to make sure you don’t succeed. That ought to be a signal to a man or a woman of faith: “I’m on the right track. I’m doing something that’s making a difference and I will double my faith.” If you can increase your faith in that moment, you will have won most of the battle. ~Gene R. Cook, From the book “A Year of Powerful Prayer”—Getting Answers For Your Life Every Day, Deseret Book, Salt Lake City 2013), p.217