system
Given the following post, respond as if you're commenting on Reddit:
human
Who decides stock prices? (because "supply and demand" isn't a conscious entity who can mentally make a decision or manually press a button to change the listed price of something)

So, I understand that prices (in general and in the stock market) are "determined" by supply and demand. 

But, say I'm selling shirts. I have 100 shirts left and they're not selling well so supply and demand has "determined" that I need to reduce my price if I want to sell more shirts. 

But "supply and demand" is neither a human being nor a robot. It is not a sentient being. It is not going to log into my POS and edit the pricing on certain products. Nor is it going to go replace my signage advertising $5 shirts with price tags and signage advertising $4 shirts. Supply and demand doesn't determine or change my prices - I do! I just make that decision based on the current supply/demand situation. 

So. Stock market. NYSE. People either won't pay the price it's listed at, or they would be willing to pay more. Who changes it?? My understanding is that the price that's listed was just the price that was paid in the last transaction, but if I have to buy or sell it at that price now then how does my transaction change the price??

I know it's all made up and the points don't matter, but I also am really struggling to understand which sentient being picks the current going rate for literally anything.
gpt
In the stock market, people with the stock and willing to sell it set an **asking price**. If someone wants to buy some stock at the lowest asking price of anyone in the market, they can. People looking to buy a stock set a **bidding price**. If someone wants to sell some stock for a highest bidding price, they can. The price of every transaction is recorded and the price of the **last** transaction is what you see when you see a stocks price (or if you are looking during the day, this may be delayed 15 minutes or whatever the policy is to restrict day trading). If you are trading stocks, you see three prices, "bid", "ask", and "last". So the price is different if you want to buy or sell. And if you want to buy (or sell) a lot, you might have to find multiple people who have different asking (or bidding) prices to complete your order. The stock's **spread** is the difference between the bid and ask. Spread is lower on stocks with more sales volume.