The congregation of God's children may not all be able to prophesy, but they know the Father's voice, and can recognize something that is just a forced performance. Musicians and prophets alike can become good fakers. They learn to cover over a lack of spirit with their own excellence. The instant a prophet allows his own excellence to replace the anointing of the Holy Spirit, he's sunk. No good thing comes from the flesh.
Human excellence is flesh.
We can't do it alone, and he won't let us just 'kick back' and watch him do everything. The worst thing the congregation can do to the prophet after the service is to tell him what a great word an unanointed prophecy was. Admire his courage. There doesn't have to be rebuke. The truth reverberating in his heart rebukes him.