You do understand it. There’s an extra mental benefit to “getting a deal”, so when you’re weighing the pros and cons that’s another thing in the “pro” column. Also, people subconsciously think expensive items are better. So this combination of higher original price and high discount makes you think you’re getting a good quality item at a deal.

You are not immune unless you do a lot of garment making and can tell the actual time and effort that went into the item you’re looking at.