https://freakonomics.com/podcast/uber-economists-dream/

Listen to this 40 minute podcast,

In the podcast, the author makes the point that he was not able to observe the demand curve he wanted, but rather was able to see an "instantaneous demand curve". In other words, he was only able to see what the demand curve for ride services looked like for one snapshot in time. The problem is that in reality, these demand curves are moving around (or increasing and decreasing) all of the time. When focusing on Uber, what are some reasons that these demand curves may be constantly shifting? Give a specific example of something that would be moving the demand curve and how it moves it.