Cold feet is apprehension or doubt strong enough to prevent a planned course of action.
The origin of the term itself has been attributed to American author Stephen Crane, who added the phrase, in 1896, to the second edition of his short novel, A Girl of the Streets.
The behaviour may be modelled as a tension between temptation and self control. If pessimism increases as the point of no return approaches then the individual may balk and refuse to proceed. If they proceed regardless then buyer's remorse is the similar feeling experienced after the event.