If you mean time spent, then yes, about 95% of time spent learning is doing. But you're talking about the cost, not the benefit. Learning by doing is very inefficient. You gain much deeper knowledge, but it can only possibly be in a very narrow area. If you spend only 5% of your time reading/listening/watching stuff, this more than pays for itself. You don't need to have experience programming a network stack before knowledge of it becomes useful. For almost everyone out there, knowledge is enough.