CoT asks the model to reason step-by-step before answering, dramatically improving accuracy on complex tasks.
# Without CoT (wrong)
Q: A train travels 120km in 1.5 hours, then 80km in 1 hour.
What is the average speed for the whole journey?
A: 100 km/h (INCORRECT)
# With CoT (correct)
Q: [same question] Let's think step by step.
A: Step 1: Total distance = 120 + 80 = 200 km
Step 2: Total time = 1.5 + 1 = 2.5 hours
Step 3: Average speed = 200 / 2.5 = 80 km/h
Answer: 80 km/h
# Zero-Shot CoT triggers:
'Let us think step by step.'
'Think through this carefully before answering.'
'Show your reasoning then give the final answer.'
'Walk me through the solution.'
# When CoT helps most:
# Math word problems
# Multi-step logic
# Commonsense reasoning
# Code debugging