Why is the total resistance of the series circuit larger than any one of the partial resistances? Why is the total resistance of the parallel circuit smaller than any one of the partial resistances

Why is the total resistance of the series circuit larger than any one of the partial resistances? Why is the total resistance of the parallel circuit smaller than any one of the partial resistances

Total resistance in series R = R 1 + R 2 + R 3 +. Of course R is greater than each resistance; parallel 1 / r = 1 / R 1 + 1 / R 2 + 1 / R 3. It's hard to understand here. You can give examples, such as setting several resistance values at will: R 1 = 2, R 2 = 3, R 3 = 4, then r = 12 / 13, smaller than each one