You are a good friend. I'm sure your friend thinks his work is good and he is willing to invest in bringing it to life. But I wouldn't be in a hurry if I were him. You're right. I suggest you study the information about mvp vs prototype. These all stages of development will help your friend understand what else can be added to the product or what to remove unnecessary. I wish you the best of luck to change your friend's mind.

If your friend has already spent a lot of time on his business plan and doesn't want to make any changes, it might be difficult to change his mind. However, here are some tips that may help you convince him to get a diagnosis or at least consider making some changes:
1. Explain the benefits: Let him know that getting a diagnosis can help him identify any weaknesses or gaps in his business plan and address them before launching the business. This can save him a lot of time, money, and frustration down the road.
2. Share success stories: Share stories of other entrepreneurs who have benefited from a business plan diagnosis and made changes that resulted in greater success.
3. Offer to help: Let him know that you are willing to help him review his business plan and provide feedback. This can be a great way to encourage him to be more open to making changes.
4. Show him the data: If there are statistics or research that support the need for a strong business plan, share them with your friend. This can help him see the importance of having a solid plan in place.
5. Be supportive: Ultimately, your friend may need to make his own decisions about his business plan. Be supportive of his choices, but let him know that you are there to help if he ever changes his mind.

Remember, getting a diagnosis for a business plan is a common practice among successful entrepreneurs, and it can help set your friend up for greater success in the long run.