Mentally contrasting a desired future with present reality fosters selective goal pursuit: People pursue feasible desired futures and let go from unfeasible ones. We investigated whether people spontaneously use mental contrasting when the demand to act toward their desired future is high. Study 1 provided correlational evidence: The participants who planned to act most immediately were also those who used mental contrasting. Studies 2 and 3 added experimental evidence: Imagining an immediate (vs. no immediate) action and being confronted with the opportunity to perform an instrumental (vs. noninstrumental) action, respectively, led participants to mentally contrast. The findings have theoretical implications by suggesting that people initiate mental contrasting as a problem-solving strategy; they have applied implications for interventions teaching mental contrasting.