The quality control (QC) process of inspecting a shirt has one main function. It ensures that the shirt was constructed according to the specifications of the shirt designer.
Does the shirt have two equal sleeves? Yes, it does.
Are the buttons sewed on firmly? Yes, quite firm.
Are there holes for the collar-stays? Yes, there are.
Are the threads trimmed? Yes, they are.
A majestic QC sticker is placed in the most precarious spot of the shirt when it passes the QC process. Congratulations, shirt!
Now consider this:
Would it be right to conclude that every shirt which appropriately earned a QC sticker is a sellable shirt?
The QC process doesn’t verify that the shirt color is ugly as sin. It doesn’t ensure that the moisture-wicking technology is superior. It doesn’t verify that the shirt fits excellently for a size. It doesn’t determine that the price is right.
Guess what a shirt designer does when he wants to know if his shirt is sized well. Or if the color is pleasant. Or if the moisture-wicking technology functions right. Or if the price-point is appropriate.
He does research and prototype testing.
He talks to people about the color. He works with a fit model. He has adventurers test out the moisture-wicking. He tests his ideas of price-point.
In doing so, he avoids the costly risk of making shirts that no one wants.