  Measuring the impact and success of human performance is common in various
disciplines, including art, science, and sports. Quantifying impact also plays
a key role on social media, where impact is usually defined as the reach of a
user's content as captured by metrics such as the number of views, likes,
retweets, or shares. In this paper, we study entire careers of Twitter users to
understand properties of impact. We show that user impact tends to have certain
characteristics: First, impact is clustered in time, such that the most
impactful tweets of a user appear close to each other. Second, users commonly
have 'hot streaks' of impact, i.e., extended periods of high-impact tweets.
Third, impact tends to gradually build up before, and fall off after, a user's
most impactful tweet. We attempt to explain these characteristics using various
properties measured on social media, including the user's network, content,
activity, and experience, and find that changes in impact are associated with
significant changes in these properties. Our findings open interesting avenues
for future research on virality and influence on social media.
