1 Thessalonians 5:21 (KJV) Prove all things; hold fast that which is good.

Here we are encouraged to not just believe whatever people say or do but to verify and test it to see it it is of GOD or not. Then when we have determined that we hold on to that which is good, comes from GOD, and let go of that which is not.
“1 John 4:1 (KJV) Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.”
“1 Corinthians 14:29 (KJV) Let the prophets speak two or three, and let the other judge.”

We are all people and the even the most anointed/gifted/sanctified/mature person can make mistakes. “1 Chronicles 17:2-4 (KJV) Then Nathan said unto David, Do all that is in thine heart; for God is with thee. [3] And it came to pass the same night, that the word of God came to Nathan, saying, [4] Go and tell David my servant, Thus saith the LORD, Thou shalt not build me an house to dwell in:” (we might look at this scripture a bit more later on)

For example when we there is a word from a prophet or a teacher teaches us something out of the bible we are to check it out ourselves by the Holy Spirit. The Holy Spirit is our teacher. “John 14:26-27 (KJV) But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. [27] Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid.”.
The Holy Spirit will confirm the Word and GOD also uses His peace to guide us. When we see that what we heard or saw some don’t match up to the truth then we ignore it, but if it is confirmed to be the truth we hold on to it and apply it in our life.

For more on this topic have a look at “do-not-believe-every-spirit”