Why does this O(n^2) code execute faster than O(n)? [duplicate]

Consider:

• f₁(n) = n²
• f₂(n) = n + 1000

Clearly f₁ is O(n²) and f₂ is O(n). For a small input (say, n=5), we have f₁(n) = 25 but f₂(n) > 1000.

Just because one function (or time complexity) is O(n) and another is O(n²) doesn’t mean that the former is smaller for all values of n, just that there is some n beyond which this will be the case.