What to do if you are disciplined, diligent and hardworking, but you can't do anything?
You need to think about the reasons for this situation. Diligence, discipline and diligence are very important. However, this is only one side of the process and such qualities in themselves, without other factors, are not the key to success. For example, you can make a huge effort, work around the clock, but your actions will focus on the little important aspects of the work. That is, in the short term, you can see just success, but from month to month, year to year you do not see progress in the long term.
From this side you need to think - what exactly you want and where you are going! What do you expect the development prospects, what is the ultimate goal. After that it will be easy to get the answer "why" you are doing this or that part of the process and to see that (maybe) some of your actions are empty and do not lead to long-term goals, which means that they should be excluded and focused on those that will help you move forward to the goals you have set. And if so - you can just get away with everything, even in a short-term scenario, because your subconscious as if "against" what and how you do. It already knows that this is the wrong approach and not what you really need.
The second point is that we are all different and have different predispositions to certain activities. It is extremely important to choose the right one. The work that is relevant to you and will develop exactly your needs and capabilities. Just hardworking and diligent people often fall into the trap of the wrong sphere. When at the expense of these qualities they can most effectively do "not their own business", and in the long run develop in the wrong direction, and not as effectively as they could. Be sure to evaluate what exactly you do and how it relates to you. Perhaps just a change of occupation will be the key to effective and rapid development and success.
To sum up, I would like to recall a quote attributed to Steve Jobs (perhaps these are his words, but I'll be honest - I never checked): "You have to work not 24 hours a day, but with your head". This is a very important approach, which is worth carrying with you all your life. Because it reflects how much more important "what" and "how" you do, rather than how much time and effort you spend on the process. And sometimes much less effort, with the right approach, can lead to much greater results.