Write a Python function `common_element(list1, list2)` that takes two lists as input and returns `True` if they have at least one common element, otherwise returns `False`.
#### Example Usage
```python [main.nopy]
print(common_element([1, 2, 3, 4, 5], [5, 6, 7, 8, 9])) # Output: True
print(common_element([1, 2, 3, 4, 5], [6, 7, 8, 9])) # Output: False
print(common_element(['a', 'b', 'c'], ['d', 'b', 'e'])) # Output: True
```
#### Requirements
- The function should iterate through the elements of both lists to determine if there is any overlap.
- The function should return a boolean value (`True` or `False`).