Classify the following phrase as a metaphor or a simile: "Life is a rollercoaster".
The phrase "Life is a rollercoaster" is a metaphor.
Complete the following task based on the instruction and optional input provided.### Instruction:
Classify the following phrase as a metaphor or a simile: "Life is a rollercoaster".

### Output:
The phrase "Life is a rollercoaster" is a metaphor.