Motivation not improved by multiple motives.

Wrzesniewski et al. do an interesting study of 11,320 West Point cadets over a period of ten years.

Although people often assume that multiple motives for doing something will be more powerful and effective than a single motive, research suggests that different types of motives for the same action sometimes compete. More specifically, research suggests that instrumental motives, which are extrinsic to the activities at hand, can weaken internal motives, which are intrinsic to the activities at hand. We tested whether holding both instrumental and internal motives yields negative outcomes in a field context in which various motives occur naturally and long-term educational and career outcomes are at stake. We assessed the impact of the motives of over 10,000 West Point cadets over the period of a decade on whether they would become commissioned officers, extend their officer service beyond the minimum required period, and be selected for early career promotions. For each outcome, motivation internal to military service itself predicted positive outcomes; a relationship that was negatively affected when instrumental motives were also in evidence. These results suggest that holding multiple motives damages persistence and performance in educational and occupational contexts over long periods of time.

Here is a bit more detail from the start of the results section:

Across two different survey measures administered by the institution at the start of their first year, cadets indicated how much each of a set of reasons offered represented their reasons for attending West Point, which allowed them to endorse any number of reasons at various levels of strength (response scales for the two measures ranged from very important to not important on a 1–3 Likert-type scale; and very positive to very negative on a 1–5 Likert-type scale). Reasons offered in the survey ranged from the prospect of getting a good job (instrumental), to economic necessity (cadets do not pay tuition), to a desire to be an Army officer (internal). Of the various reasons offered, two types were of key interest: reasons indicating an internal desire to become an Army officer and reasons indicating an instrumental desire to gain eventual outcomes associated with attending West Point. The data are archival; thus, none of the items in the surveys completed by cadets perfectly captured the distinction between “internal” and “instrumental” motives. For example, there were no items intended to capture a “pure” internal motive, defined to mean that the activity of becoming a West Point cadet was a meaningful and valuable end in itself (3). However, this motive is “internal” in the sense that the desire to be an Army officer requires that one do the things that Army officers do. In this way, it is akin to “being a soldier” (internal) rather than “getting a good job” (instrumental)....A total of 31 reasons appeared in the surveys and were subjected to exploratory factor analysis...