Practice refines technique
10,000 hours of watching YouTube tutorials on how to sketch doesn't replace 10,000 hours of practice.
Consuming good direction helps to create. Mindlessly sketching every day without worrying about perspective won't improve anyone's abilities much. Yet, sketching with good advice in mind will.
Tutorials help with the approach to sketching, practice refines technique.
Robert Kiss has a great playlist of YouTube videos for fundamental sketching techniques.