Mē is the subjective or conditional negation particle in Greek, as opposed to ou/ouk/ouch which negates objective facts. Mē appears about 1,042 times and is used with subjunctive, optative, imperative, and infinitive moods — any context involving will, wish, command, purpose, or possibility. It negates what is not the case from the speaker's perspective or in hypothetical situations.
The distinction between ou (objective negation) and mē (subjective/volitional negation) matters theologically. When Jesus says "Do not (mē) be afraid" (Matthew 14:27), it is a command to stop letting fear control the will — not an assertion about external circumstances. Paul's "by no means!" (mē genoito) in Romans 6:2 is the strongest possible volitional negation — "may it never be!" This precision in negation reveals Scripture's nuanced view of human will, divine command, and the nature of faith.