Dudley's answer is more descriptive, but, simply put, it's all about
pitch attitude and airspeed for the aircraft's weight at landing.
Each time you fly, you are probably at a different weight. That varies
the actual landing speed by a few knots. It also changes the amount of
pull on the yoke to get the proper pitch attitude to fly at the proper
speed for that weight.
If you use the same numbers for when the whole family is flying vice for
those times when it is just Mary and you, you will probably be too fast
and float.
Wind also comes into play, but that is different with each flight.