I recent went shopping for smart casual clothes along with a friend. His knowledge of fashion was far greater than mine and he pointed out things like this item is too young for a nearly 40 year old; item X has to be matched with item Y but will not go with item Z; you often have to buy a complete outfit rather than individual items to add to things already in your wardrobe. He also had detailed knowledge of trainers saying things like these are running shoes and these are chilling shoes; this item is worn with jeans and will not go with a tracksuit and vice versa.
I then asked him where he got all this knowledge from but he couldn't really explain. He made out that he just picked it up as he went along in life. Where exactly to people who know about fashion learn it from?
Had I gone shopping on my own then I would probably have come away with a completely different items to the ones I purchased. Historically I just used to buy clothes that appealed to me visually or thought would be appropriate for an occasion - even if they weren't. With hindsight, I have probably mismatched two or more otherwise good items many times when dressing. I also had a preference for more 'neutral' clothing and dislike buying certain designer brands or items that are likely to go out of fashion quickly.