The term motivation is from 1873, "act or process of furnishing with an incentive or inducement to action. Perhaps borrowed from German, where motivation is attested by 1854. Psychological use, "inner or social stimulus for an action," is from 1904.
Why is your counterpart engaging in negotiations? Solid preparation for a negotiation requires probing and collecting information to gain a more complete understanding of both party's motivation. Why are they acting as they do? We also need to understand why we, including our team, are acting as we do. Motivation is the “why” and objectives are the “what.” Negotiators should use incentives and penalties to get to a positive resolution.