Matthew 13:24-29 (KJV) 24 Another parable put he forth unto them, saying, The kingdom of heaven is likened unto a man which sowed good seed in his field: 25 But while men slept, his enemy came and sowed tares among the wheat, and went his way. 26 But when the blade was sprung up, and brought forth fruit, then appeared the tares also. 27 So the servants of the householder came and said unto him, Sir, didst not thou sow good seed in thy field? from whence then hath it tares? 28 He said unto them, An enemy hath done this. The servants said unto him, Wilt thou then that we go and gather them up? 29 But he said, Nay; lest while ye gather up the tares, ye root up also the wheat with them.
Evidently, we cannot tell the unfruitful from the false. Otherwise, Jesus would not be concerned that while segregating the wheat from the tares, we might incorrectly remove the wheat.