Haruki Murakami, the excellent Japanese novelist, wrote about the sign inside his Japanese gym. It was something like,
"Fat is easy to get and hard to lose. Muscle is hard to get and easy to lose. Such is life."
It's similar to another Japanese expression about money --
"Getting money is like digging in sand with a needle, spending it is like water soaking into sand."
I remember where I read the first quote -- it was reading "What I Talk About When I Talk About Running" in 2008, when I was in Barcelona and living near Placa Espania. At the time, I happened to be on a fantastic routine of waking up at 4:30AM, reading and eating in a little Spanish shop that served a fantastic Spanish egg/potato/vegetable omlette until my gym opened, spending a couple hours in the gym, and then working until dinner before sleeping early.
From the WIkipedia entry on Upaya in Buddhism, translated into English roughly as "skillful or expedient means to an end" --
"Shariputra, suppose that in a certain town in a certain country there was a very rich man. He was far along in years and his wealth was beyond measure. He had many fields, houses and menservants. His own house was big and rambling, but it had only one gate. A great many people--a hundred, two hundred, perhaps as many as five hundred--lived in the house. The halls and rooms were old and decaying, the walls crumbling, the pillars rotten at their base, and the beams and rafters crooked and aslant. At that time a fire suddenly broke out on all sides, spreading through the rooms of the house. The sons of the rich man, ten, twenty perhaps thirty, were inside the house. When the rich man saw the huge flames leaping up on every side, he was greatly alarmed and fearful and thought to himself, I can escape to safety through the flaming gate, but my sons are inside the burning house enjoying themselves and playing games, unaware, unknowing, without alarm or fear. The fire is closing in on them, suffering and pain threaten them, yet their minds have no sense of loathing or peril and they do not think of trying to escape! "Shariputra, this rich man thought to himself, I have strength in my body and arms. I can wrap them in a robe or place them on a bench and carry them out of the house. And then again he thought, this house has only one gate, and moreover it is narrow and small. My sons are very young, they have no understanding, and they love their games, being so engrossed in them that they are likely to be burned in the fire. I must explain to them why I am fearful and alarmed. The house is already in flames and I must get them out quickly and not let them be burned up in the fire! Having thought in this way, he followed his plan and called to all his sons, saying, 'You must come out at once!" But though the father was moved by pity and gave good words of instruction, the sons were absorbed in their games and unwilling to heed them. They had no alarm, no fright, and in the end no mind to leave the house. Moreover, they did not understand what the fire was, what the house was, what the danger was. They merely raced about this way and that in play and looked at their father without heeding him. "At that time the rich man had this thought: the house is already in flames from this huge fire. If I and my sons do not get out at once, we are certain to be burned. I must now invent some expedient means that will make it possible for the children to escape harm. The father understood his sons and knew what various toys and curious objects each child customarily liked and what would delight them. And so he said to them, 'The kind of playthings you like are rare and hard to find. If you do not take them when you can, you will surely regret it later. For example, things like these goat-carts, deer-carts and ox-carts. They are outside the gate now where you can play with them. So you must come out of this burning house at once. Then whatever ones you want, I will give them all to you!' "At that time, when the sons heard their father telling them about these rare playthings, because such things were just what they had wanted, each felt emboldened in heart and, pushing and shoving one another, they all came wildly dashing out of the burning house."