This is a simple question with a not-so-simple answer.
First, to progress on this path, "Brutal Self-Honesty" is required. Partner training helps you avoid devusion and lets you see clearly... You may 'believe' that your skill level is improving, but you won't really 'know' until you touch another person.
More importantly, when you train with others who are working the same principles and curriculum as you are, improvement occurs much faster than when practicing solo. It is said that 'A Rising Tide Lift All Boats'. Without partner training, you cannot progress beyond a superficial understanding.
It is also said that 'Consistency = Knowledge' and that 'Understanding comes from Doing'. Understanding the Internal takes 4 hands.
The rule of thumb is 80/20. For every 80 minutes of solo practice you want to get a minimum of 20 minutes partner practice.




