Gil Carlson, who was the first person to come up with many of the hydronic concepts we take for granted today, was also my teacher. He would often say, “For a difference to be a difference, it has to make a difference.” It popped out most of the time at seminars when someone (nearly always an engineer) wanted to pick hydronic nits with him. That nearly famous quote shut most people up.
Gil, when explaining how cutting corners is usually folly, would also say, “What you save on the roast beef, you spend on the mashed potatoes.” That one made me pause when I first heard it, but I was young and liked to eat a lot. The lesson eventually sunk in.