Think about the last time you bought a piece of clothing for someone else. Who was it that you were shopping for? I bet it was someone you know well – maybe your partner, child, sister, or best friend.
Picking out clothing for someone else requires you to know their personal style, preferences, and size. It is kind of intimate in this way. Without some sort of relationship and familiarity, it would be hard to know what to get. The more you know the person, the easier it is to confidently choose something that will delight them.
This is just as true for designing clothes for someone else as it is for shopping for someone else. Designing clothes requires a relationship with the people you are dressing. You have to get to know them and their preferences, know their size, and remember their favorite color.
Only when you have this kind of familiarity with your customers can you create something they will love.