Why don’t light particles just travel wherever they want? How does light fade and create shadows?

Question: Why don't light particles just travel wherever they want? How does light fade and create shadows?
- Keywords:
  fade,
  light,
  particle,
  shadow
Asked by Lily to Adele on 12 Jun 2017.
- Adele Wratten answered on 12 Jun 2017:
  
  Shadows are created when light gets blocked out by something, like a person or object. So light can travel in different ways, like it does with rainbows!

Question: Why don't light particles just travel wherever they want? How does light fade and create shadows?