If I swam ten lengths a day, after five lengths I would say to myself, "I've managed $\frac{5}{10}$ of my day's swimming - that's $\frac{1}{2}$!" After eight lengths, I would say I'd done $\frac{8}{10}$, which simplifies down to $\frac{4}{5}$. After nine lengths, I'd say I'd done $\frac{9}{10}$, which does not simplify.