投

Well, you usually use your fingers to throw objects used as missile weapons. Easy. By the way, for those of you looking for a less anachronistic image for the missile primitive as a modern rocket, try a slingshot. it's a crotch (originally a tree branch) that sends missile projectiles flying into/like the wind. And for this present kanji, it is something you naturally use with your fingers...

Source: Kanji Koohii community