A frog will boil to death if it is put in a sauce pan with cold water on a stove and the heat is slowly increased. The frog will not notice the increase in temperature until it is too late.
Same thing happens with our expenses. Slowly as we get promoted and become more successful our expenses also increase. We move into a better apartment. We buy a better car. We upgrade our wardrobe. We even upgrade or change our spouses. Sooner or later we find ourselves living unsustainable lifestyles with nothing to show for all our hard work.
This phenomenon is called lifestyle creep and we need to become aware of it so that we can control it.