In a preregistered ecological momentary intervention study, we alternately instructed participants to adopt an upward and downward comparison focus. In all, 349 participants reported 8,137 social comparison situations across 6 days and three comparison conditions (baseline, upward, downward). For each comparison, participants reported social comparison direction, motivation, effort intentions, and emotions in five daily reports and one daily end-of-day summary. As predicted, an upward comparison focus resulted in more self-improvement motivation (pushing) and more negative emotions, whereas days with a downward comparison focus resulted in decreased motivation (coasting) but more positive emotions (vs. baseline). However, at the end of the day, people experienced lower goal approach on upward but higher goal approach on downward comparison days. Hence, engaging in strategic upward comparison was motivating in the short term but resulted in surprisingly opposite effects at the end of the day. We offer possible explanations from cognitive and motivational perspectives.