If what a prophet proclaims in the name of the Lord does not take place or come true, that is a message the Lord has not spoken. That prophet has spoken presumptuously. Do not be afraid of him. (Deuteronomy 18:22)
Even these days, there are many who go about prophesying this and that, but rarely do the things that they proclaim really happen. Of course, they have explanations for the things not happening as they said, but God here very clearly warns his people that there are so called prophets who speak presumptuosly in the name of the Lord. One has to be careful when dealing with prophets and prophesy.
There are genuine prophets and servants of God who minister in the prophetic, but they are few. A piece of advice from the Apostle Paul to the Church in Thessalonica says,
Do not treat prophecies with contempt. Test everything. Hold on to the good. (1 Thessalonians 5:20, 21)
A word to exercise caution from Jesus too..
"Watch out for false prophets. They come to you in sheep's clothing, but inwardly they are ferocious wolves. By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles? Likewise every good tree bears good fruit, but a bad tree bears bad fruit." (Matthew 7:15-17)
So let us be careful, for these things can make or break our lives.