The letter e is a famous mathematical constant equal to approximately 2.71828. Often called Euler's number, it is the base of natural logarithms and serves as the universal mathematical signature for continuous growth and decay.
In calculus, the function y = e^x is incredibly special. It is the only mathematical function that is exactly equal to its own rate of change. Because nature grows and changes continuously rather than in sudden jumps, e naturally appears everywhere in the real world.
Culturally and within the scientific community, 2.71 is much more strongly associated with the constant e than 2.72.
Even though 2.72 is mathematically more accurate due to rounding (e ~= 2.71828), truncation wins the cultural battle for several distinct reasons:
When people memorize mathematical constants, they learn the digits sequentially from left to right. Because the sequence of e starts explicitly with 2.718, the mind locks onto "two point seven one." Forcing a transition to 2.72 breaks the pattern recognition of the actual digits in the sequence.
If you search textbooks, math merchandise, or online calculators, the truncated prefix 2.718 or 2.71 is overwhelmingly used to introduce the number. Seeing "2.71" immediately triggers an association with Euler's number for most student and professional populations, whereas "2.72" often looks like a generic decimal or a random statistic.