She made a false step by trusting the wrong person.
error
Frequency:
60
%
It was an error that led to his false step in the project.
slip-up
Frequency:
40
%
The slip-up was a false step that could have been avoided with more caution.
Idiomatic Expressions for false step
Phrase: be on the lookout for false steps
Meaning: to be cautious and vigilant for mistakes or errors
Usage: In such a high-stakes game, you need to be on the lookout for false steps from your opponents.