In a study of children, researchers wanted to assess how mood effected goal-setting and performance.
It was predicted that goal level would drive performance but the results said otherwise... Researchers induced either a happy or sad mood through asking children to think of happy or sad thoughts for a minute. Then they gave them a set of a simple problem solving tasks and asked them how many they thought they would complete in five minutes. Then they worked for five minutes and tallied the results.
A happy mood led to setting significantly higher goals and superior performance.
A similar study looking at negative, neutral, and positive mood found facilitated learning and performance while sad mood hindered it all relative to neutral.
REFERENCE
Hom, H.L., Arbuckle, B. Mood induction effects upon goal setting and performance in young children. Motiv Emot 12, 113–122 (1988). https://doi.org/10.1007/BF00992168
Masters, J. C., Barden, R. C., & Ford, M. E. (1979). Affective states, expressive behavior, and learning in children. Journal of Personality and Social Psychology, 37, 380-390.