After determining WHO should buy your product, you have to answer the question WHY these people would buy your shirt. Ask yourself:
With this approach you can identify a niche. Therefore, you need to examine the market (the t-shirt market in this case) with regard to your target group. A lot is already available, but by far not everything. And this is YOUR chance.
Your product should be unique. Rule of thumb:
This is the reason why it is so important that you really KNOW your target group! A Bavarian woman in her forties with a passion for knitting would hardly have sufficient knowledge of the target group which we have defined earlier.
Do you have an idea? Then ask yourself:
Be honest to yourself. Of course, you can also ask family and friends for advice. Especially, if these people belong to the target group, that you have selected.
This question could help you: