How can supply actually change the value of something

Supply and demand play a huge part in the value of someting for a consumer. When there is a low supply of an item and the item is in high demand, the value you seems to go up for a consumer because they have to have it. The want for an item that may not always be there is what brings value to the consumer and in some cases, have them purchase the item just because of the chance of it running out. When there is a large supply of an item, the value may not be as much to a consumer because they think they can purchase the item whenever they want.