Final answer:
Externally-provided rationales work as a motivational strategy during uninteresting activities by increasing internalization, valuing, and identified regulation.
Step-by-step explanation:
The reason an externally-provided rationale works as a motivational strategy during an uninteresting activity is because it can increase internalization, valuing, and identified regulation. This means that when a person is given a reason or explanation for why an activity is important or meaningful, they are more likely to internalize and value the activity, which leads to higher motivation. This is supported by research that shows that providing students with a rationale for engaging in learning activities can enhance their intrinsic motivation for those tasks (Niemiec & Ryan, 2009).