All men are liable to error; and most men are, in many points, by passion or interest, under temptation to it.

Locke underscores human fallibility as a universal condition: error is not an exception but a standing possibility for everyone. He then sharpens the point by identifying why error persists—people are often pulled off course by “passion or interest,” meaning strong emotions, factional loyalties, self-advantage, or social pressures that bias judgment. The remark functions as a caution against intellectual arrogance and as an argument for epistemic humility: because our reasoning is vulnerable to motivated distortion, we should be wary of dogmatism, seek evidence, and remain open to correction. In political and religious disputes, it also implies the need for tolerance and fair procedures, since sincere people can be wrong for predictable human reasons.