system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does something become a commodity and what does that mean for public access to the item - like water, gold etc?
gpt
Generally commodities are less expensive than otherwise due to the greater competition between suppliers. If you want gold then any gold will do from anyone who has it, but if you want an iPhone only Apple can produce it.

Of course this doesn't mean that a commodity is inexpensive overall, gold being an example. It just means there aren't any differentiating features between one supplier and another.