Exaggeration as a way to prove or disprove statements relies heavily on "common sense". Now, "common sense" is a bad advisor in this field because we don't do atom tracking in our daily life. After all, common sense suggests that Sun is going around Earth. So, we have to count if we are looking for a great price/quality ratio (as JohnG did here), or, if we only care about precision, measure (see the report of Ratan D. Bhardwaj in the Proceedings). However, we should define our terms before we start any calculations/measurements. Lets use analogy*. Here is a similar question:"Most of the car get replaced (a) in 1 year, (b) in 10 years, © never? (a) Is correct, because the car burns10 gallons of gas every week. 10 US gal/week x 6.073 Lb/US gal x 52 weeks/year = 3150 Lb/year**. So, Ford Focus (2641 Lb) consumes more gas then it weights in one year. For a dramatic result lets consider a container with water. Does it mostly change or mostly remains intact once we empty the container? Well, it depends whom you ask. Archeologist would say: "this ancient vase that we came upon at the bottom of the sea didn't lose any when we dumped water out of it". A traveler, parched with thirst and dying in a desert (with an empty canister) believes that a bottle of water is quite different from an empty bottle. Note that a bottle doesn't have to become "a horse a man or a woman" (b) Is correct, because quite a few parts were replaced. Also, if you have to choose between two cars (same make, same model, same price, but different year) you will likely go for this year, than a 10 year old car. And, yet, it is the same car. © Is also correct, because we can draw a continuous line through space-time that connects the new and the old car. So, the question translates into "who am I and what are the necessery and sufficient components of me" everybody answers this question differently, hence the numbers vary". Measurement of flux (replacement of material over some period of time) gives the half-life: intrinsic value with a clear physical meaning, but this value upsets the subjects of the research. As subjects we want this value to be higher. Why higher (and not lower)? I would speculate that humans realize that they change very fast. "Yesterday-Me" was drunk and happy, as a result "Current-Me" (which is the real me, because Current-Me perceives the world) has a hangover. And has to work so that "Tomorrow-Me" had some results to report to boss/client and "Year-Later-Me" got bonuses and longer vocation. Yesterday-Me is a mean guy because when he enjoys life Today-Me suffers. Future-Me is elusive (there is no guarantee of any kind, not even that "Year-Later-Me" will live). So, should I work for some vague guy in future if I can do something pleasant now? This idea is very old. You might recall that criminals in ancient Greece argued that the crime was committed by some other guy (Earlier-Me), so, why should Today-Me be punished? Clearly, these questions are counterproductive and dangerous to both the "philosopher" and his neighbors. As a result, people started to convince each other that you are the same person from birth to death. Arguments were simple: yes, your habits, manners, and behavior gradually change, but the body remains the same. Well, size changes, proportion change too .. but (ace of trump) you form a continuous line in space-time. The idea that body remains the same became a dogma. Nowadays we work for better tomorrow because we logically understand that we should and because we suppress feelings (the feelings suggest to enjoy life now) with the "same body" dogma. When one suddenly*** discovers that his body changes quite fast his carpe diem attitude surfaces. Some people give in and die out, others experience pain in the lower part of the back, but bite the bullet, go into denial, and win the evolutionary race. PS. Peacocks lost the ability to fly, because females choose males with the biggest and brightest tail. This is a loosing strategy for the whole population. Losing ability to fly for nothing is a bad deal. Yet, this is a great strategy for females (her male offspring will have huge tale and will reproduce. Classical Pronzi scheme in animal world. It is theoretically possible, peacocks can all agree that flight is a good thing and they should choose male partner based on his flight, not his tail. However, it is not feasible. Similarly, humankind selected those who rest less and "works" for future more (here "works" includes "steal", "take part in raids", and, especially "organize raids"). The most active won competition within the groups. The group of the most active "builders of better tomorrow" won the evolutionary race in against other groups. Simply put they slaughtered natives and grubbed their land. Currently, there is no evolutionary benefit for humankind to work harder and harder. The results of harder work will anyway be destroyed in the economic (overproduction) crisis. In principle, humans could have agreed to balance their work and rest time... But in reality we are no better then peacocks in this delicate question. Hence, the struggle between carpe diem and "the builder of better tomorrow" will continue and topic-starter's question will touch people's hearts. _____ * Analogy is not for everyone foolproof... But we don't have much options on this stage. There are copious procedures to solve problem (see "Materials and Methods" section in any scientific paper); but what standard methods do we have to notice/cognize and state/formulate a problem? **Given the accuracy of gas consumption estimate (plus or minus two-fold) there is no point to copy all four digits in density constant. *** For this discovery one needs to know how much water+food he consumes daily, divided by the weight of his body.