a WHOLE always simplifies to one, and whole occurs when the numerator and denominator are equal, say 4/4, 5/5, 1000/1000, 19/19, 1000000/1000000 and so on, give us a whole.
well, as you see in the multiplication above, the "4" ends up at the top or multiplying with the numerator, and that product of 4*1 is well, less than the denominator, a fraction with a denominator that's larger than its buddy atop is always less than 1.
other examples for that less than one will be, 3/4, 5/6, 999/1000, 18/19 and so on.