You can think of handily as the hand's own measure of two things: distance and effort. If something sits inside the reach of your hand, you do not have to walk for it, hunt for it, or work for it. A key kept by the door is inside that reach. So, in a different way, is a win that costs you almost nothing.
handily 可以想成用「手」在量兩件事：距離和力氣。東西如果就在手構得到的地方，你不用走過去、不用翻找、也不用花力氣。門邊的那串鑰匙在這個範圍裡；而贏得毫不費力的一場比賽，感覺上也在這個範圍裡。這個字的兩個用法，都可以想成從「伸手就到」長出來。
From the word’s history
Handily is handy plus -ly, and handy is built on hand, so the adverb sits directly on the body part.
handily 是 handy 加上 -ly，而 handy 又是蓋在 hand（手）上面的。所以這個副詞從構詞上就綁著「手」，也難怪它的用法都繞著「伸手可及」打轉。
Wiktionary etymology supplied in packet (kaikki:3f6f69a190036ae4:135589116): From handy + -ly. Compare Middle English hendily, hendiliche.
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