Remember those three monkeys: the first one has his eyes covered (see no evil); the second one has his ears covered (hear no evil); and the third has his mouth covered (say no evil).
The devil loves to use that second one -- the hearing thing. He loves to send discouragement our way, especially when we are doing what God has called us to do. If you know you are doing what you're supposed to do and you start hearing from all sorts of people, "No, no, no" you might be on the right track.
The enemy isn't picky either. He'll use anyone, especially fellow Believers.
This reminds me of the part in the book of Job when Job's friends come to visit. They had the best of intentions but their efforts to comfort turned quickly to criticism once they started speaking and trying to fix it for Job. Let me quote for you:
(from The Message Bible at http://Biblegateway.com)
11-13 Three of Job's friends heard of all the trouble that had fallen on him. Each traveled from his own country—Eliphaz from Teman, Bildad from Shuhah, Zophar from Naamath—and went together to Job to keep him company and comfort him. When they first caught sight of him, they couldn't believe what they saw—they hardly recognized him! They cried out in lament, ripped their robes, and dumped dirt on their heads as a sign of their grief. Then they sat with him on the ground. Seven days and nights they sat there without saying a word. They could see how rotten he felt, how deeply he was suffering.
If only they would have kept silent. When Job's trial was coming to an end even God rebukes his friends:
7-8 After God had finished addressing Job, he turned to Eliphaz the Temanite and said, "I've had it with you and your two friends. I'm fed up! You haven't been honest either with me or about me—not the way my friend Job has. So here's what you must do. Take seven bulls and seven rams, and go to my friend Job. Sacrifice a burnt offering on your own behalf. My friend Job will pray for you, and I will accept his prayer. He will ask me not to treat you as you deserve for talking nonsense about me, and for not being honest with me, as he has."
Sometimes some of us probably need a strong rebuke like this. Encourage those around you today, especially if you need some encouragement. God's here. He's never left. He loves you desperately.