How to diagnose sharpness issues. What causes the problem in the first place?

About

My name is Simon d'Entremont and I'm a Canon Ambassador as well as a Kase Filters Ambassador, and a nature and wildlife photographer living in Nova Scotia, Canada. I’m a photographer first, YouTuber second, and my mission is to lift the knowledge, skills, and spirits of the people around me so they can be at their best, whatever they want that to be. My favorite saying is « I know you can do it! ». And btw, ISO 12,800 is fine… Reach me at [email protected]