This could be just me, but at first glance the word (phrase?) 人一倍【ひといちばい】 looks like it would mean "one's own share of the work". I assumed 人 to mean one person, and 一倍【いちばい】 means "one share, one amount". I was a little confused to find out that 人一倍 actually means "more than others, redoubled, unusual". (For example, 人一倍働く【ひといちばいはたら】 means " to work twice as hard as others".)
Does anyone have any insight or explanation for this, or have I completely misunderstood the whole thing?
According to 大辞林, one of the meanings of 一倍 is as follows:
ある数量を二つ合わせた数量。二倍。倍。
The first example it gives includes 人一倍, so you're right that 人一倍 is the combination of 人 and 一倍. The surprising part is that 一倍 means 二倍!
As Wikipedia explains, for much of the history of Japan, 倍 was a suffix indicating a number of times in addition to one. In other words, 一倍, 二倍, and 三倍 used to mean 2x, 3x, and 4x. In modern Japanese, they generally mean 1x, 2x, and 3x, but as you've discovered, the old meaning of 倍 is not entirely gone--it's preserved in words like 人一倍.
You may also want to read the answers on this similar question in Japanese.
Snailplane-san is right. In Yedo era there were two words indicating multiple number: 倍 and [層倍]{そうばい}. A single word 倍 means two times and a single word 層倍 does one time. 2倍 means 3 times and 2層倍 is two times.
In Meiji era there comes European mathematics and the above-mentioned way to use of 倍 and 層倍 was banned.
Today we use 2倍 as two times. 3倍 means three times. But the old way to use of 倍 remains in some phrases, such as [倍]{ばい}にして[返]{かえ}す, [倍返]{ばいがえ}し and [人]{ひと}の[倍]{ばい}[働]{はたら}く. Most of us have never heard of the word 層倍.
Just like you, many Japanese wonder about [人一倍]{ひといちばい}. I must study English with sense of language like you. Good luck for your studying Japanese!
snailplane is right about her explanation.
Not sure about Nihongo but in Mandarin, the confusing one is 一倍 and 二倍 is used interchangeably. Meaning might be different at different context. So just read carefully.
