system
Given the following post, respond as if you're commenting on Reddit:
human
Why does an increase in supply reduce prices/demand?

I am reading a book on economics and it says that more supply equals less demand because people won’t pay a high price for things that are plentiful: "high supply will push prices down as consumers will not pay a premium for something that is plentiful."

But this just seems kind of non-sequitur. Why would the supply of something increasing make me value a unit of that thing less? For the sake of example, let’s say I am willing to pay X amount of dollars for a certain type of car. But then the company manufactures 100 more of these cars, making it more plentiful. Why would I suddenly not be willing to pay as much for the car I wanted just because the supply of them overall increased? 

To illustrate my confusion, this is what the sentence "high supply will push prices down as consumers will not pay a premium for something that is plentiful" is making me imagine:

Customer: I am willing to pay $50,000 for this automobile. Is this the only one of its kind you have?

Seller: Actually, no. We have 100 of that specific model in stock.

Customer: Oh, well because there's plenty of them, I'm only willing to pay $40,000 now. 

Hopefully someone sees where I'm confused and can explain what I'm missing.
gpt
Let's say you go to buy a car for $50,000. Then you notice a new car dealer has popped up. Since you're the only customer (for now) the dealer has to offer a lower price in order to get you to pick them over whomever you were originally going to buy from . So they undercut the other dealer and offer you a car for $45,000. 

The idea is that leaving cars unsold generates zero profit, so if producers want you to buy all of what they have then they have to cut prices. This is easier to understand with something like a fruit stand where the fruit expires at the end of the day and there are a lot of different sellers. If a new fruit stand enters the market they have to persuade people to buy from them and the easiest way to do that is by offering cheaper prices.