This exercise is about forcing yourself to identify the gaps in your capabilities. There's nothing wrong in having gaps in your skillset - but if you're asked to work on projects where you need that skill - it can dent your confidence or highlight a need for development.
Take a sheet of paper, or the downloadable worksheet, and list out areas you don't enjoy or feel comfortable doing. Use projects you've worked on recently to think about the roles which needed to be played. Score yourself against each area, from 0-5 (where 0 is no skills, and 5 is acceptable skills).
Keep thinking about recent projects or upcoming projects to add more and more relevant areas where you may need other people to be part of your team to deliver a piece of work
Don't feel bad about the long list of things you can't do - you're just one person!