This research demonstrates that people can act more powerfully without having power. Researchers and practitioners advise people to obtain alternatives in social exchange relationships to enhance their power. However, alternatives are not always readily available, often forcing people to interact without having much power. Building on research suggesting that subjective power and objective outcomes are disconnected and that mental simulation can improve aspirations, we show that the mental imagery of a strong alternative can provide some of the benefits that real alternatives provide. We tested this hypothesis in one context of social exchange—negotiations—and demonstrate that imagining strong alternatives (vs. not) causes powerless individuals to negotiate more ambitiously. Negotiators reached more profitable agreements when they had a stronger tendency to simulate alternatives (Study 1) or when they were instructed to simulate an alternative (Studies 3–6). Mediation analyses suggest that mental simulation enhanced performance because it boosted negotiators’ aspirations and subsequent first offers (Studies 2–6), but only when the simulated alternative was attractive (Study 5). We used various negotiation contexts, which also allowed us to identify important boundary conditions of mental simulations in interdependent settings: mental simulation no longer helped when negotiators did not make the first offer, when their opponents simultaneously engaged in mental simulation (Study 6), and even backfired in settings where negotiators’ positions were difficult to reconcile (Study 7). An internal meta-analysis of the file-drawer produces conservative effect size estimates and demonstrates the robustness of the effect. We contribute to social power, negotiations, and mental simulation research.