Here's why:

* Liquids are fluids: This means they can flow and take the shape of their container. They don't have a fixed shape like solids.

* Surface tension: Liquids do have some resistance to change shape due to surface tension, which is a force that pulls molecules together at the surface. This is why small drops of liquid are round.

* Gravity: Gravity pulls liquids downwards, making them flatten out in a container.

So, a liquid will take the shape of the bottom and sides of the container it's in.