Several content-driven platforms have adopted the ‘micro video’ for-mat, a new form of short video that is constrained in duration, typically at most5-10 seconds long. Micro videos are typically viewed through mobile apps, andare presented to viewers as a long list of videos that can be scrolled through.How should micro video creators capture viewers’ attention in the short attentionspan? Does quality of content matter? Or do social effects predominate, givingcontent from users with large numbers of followers a greater chance of becomingpopular? To the extent that quality matters, what aspect of the video – aestheticsor affect – is critical to ensuring user engagement?We examine these questions using a snapshot of nearly all (>120,000) videosuploaded to globally accessible channels on the micro video platform Vine overan 8 week period. We find that although social factors do affect engagement, con-tent quality becomes equally important at the top end of the engagement scale.Furthermore, using the temporal aspects of video, we verify that decisions aremade quickly, and that first impressions matter more, with the first seconds of thevideo typically being of higher quality and having a large effect on overall userengagement. We verify these data-driven insights with a user study from 115 re-spondents, confirming that users tend to engage with micro videos based on “firstsight”, and that users see this format as a more immediate and less professionalmedium than traditional user-generated video (e.g., YouTube) or user-generatedimages (e.g., Flickr).