After learning about the binary number system (only 2 symbols, i.e. 0 and 1), I just thought why did we adopt the decimal number system (10 symbols) after all?
I mean if you go to see, it’s rather inefficient when compared to the octal (8 symbols) and the hexadecimal (16 symbols)?
Expanding on the comment by J.M., let me quote from the (highly recommended) book by Georges Ifrah The Universal History of Numbers (Wiley, 2000, pp. 21-22):
Traces of the anthropomorphic origin of counting systems can be found in many languages. In the Ali language (Central Africa), for example, “five” and “ten” are respectively moro and
mbouna: moro is actually the word for “hand” and mbouna is a contraction of moro (“five”) and bouna, meaning “two” (thus “ten”=”two hands”).
It is therefore very probable that the Indo-European, Semitic and Mongolian words for the first ten numbers derive from expressions related to finger-counting. But this is an unverifiable hypothesis, since the original meanings of the names of the numbers have been lost.
Ifrah then goes on to explain that
…the hand makes the two complementary aspects of integers entirely intuitive. It serves as an instrument permitting natural movement between cardinal and ordinal numbering. If you need to show that a set contains three, four, seven or ten elements, you raise or bend simultaneously three, four, seven or ten fingers, using your hand as cardinal mapping. If you want to count out the same things, then you bend or raise three, four, seven or ten fingers in succession, using the hand as an ordinal counting tool.