This study examines the effect of task property feedback and the completeness of outcome feedback on decision performance and whether decision makers can diversify their choices to avoid the biased learning from incomplete outcome feedback. Recruiting 95 students as the participants in an experiment in which participants perform the product investing task. The result shows that there is a moderating effect of task property feedback on the effect of completeness of outcome feedback on decision performance. The provision of task property feedback increases the difference between performance of decision makers receiving complete and incomplete outcome feedback. The result does not support the infernece that decision makers can diversify their choices to avoid the biased learning from incomplete outcome feedback.