1/5

When you know the path in advance — "every number from 1 to 5" — managing your own counter is beneath you. for walks the sequence for you:

for n in 1..=5 {
    println!("step {}", n);
}

Each pass, n takes the next value: 1, 2, 3, 4, 5. No counter to forget, no way to overshoot.