They cannot predict the future.

28 For I look [upon the heathen prophets and the priests of pagan practices] and there is no man among them [who could predict these events], and among these [idols] there is no counselor who, when I ask of him, can answer a word.
29 Behold, these [pagan prophets and priests] are all emptiness (falseness and futility)! Their works are worthless; their molten images are empty wind (confusion and waste).
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Isaiah 41:28-29

Amplified Bible (AMP)