Most people don’t have it.
Assiduity is the skill of sitting on your ass until you solve the problem at hand.
Most people will get restless or bored with a difficult problem. Their mind will become distracted and they will focus on something else.
The art of sitting in silence with nothing but your mind and a blank canvas is intimidating. You may become discouraged, frustrated, stumped, or helpless. There will always be some form of resistance and you must face it down. You will never face it down unless it’s a problem worth solving.
You must sit with the discomfort and finish what you started.