Inability to develop myself when working with strong co-author
In order to develop your personal skills, you need to invest time, and the time that your coauthor spends on solving &quot;your problems&quot; doesn't count. The best way to use your coauthor to improve your skills  is to analyze everything they do and ask questions when you don't understand something. It's like having a free tutor (well, the price being having a coauthor)...