Background: Pair programming (PP) can have many benefits in industry. Researchers and practitioners recognize that successful and productive PP involves some skill that might take time to learn and improve. Question: What are the elements of pair programming skill? Method: We perform qualitative analyses of industrial pair programming sessions following the Grounded Theory Methodology. We look for patterns of problematic behavior to conceptualize key elements of what 'good' and 'bad' pairs do differently. Results: Here, we report two elements of pair programming skill: Good pairs (1) manage to maintain their Togetherness and (2) keep an eye on their session's Expediency. We identify three problematic behavioral patterns that affect one or both of these elements: Getting Lost in the Weeds, Losing the Partner, and Drowning the Partner. Conclusion: Pair programming skill is separate from general software development skill. Years of PP experience are neither a prerequisite nor sufficient for successful pair programming.