Like so many expressions, the source is Shakespeare. The world is your oyster is said to another person to indicate that there is a world of relatively easy opportunities and alternatives facing them, most of which will lead to gain or profit of some kind. The analogy comes from the act of opening an oyster and finding a pearl. In The Merry Wives of Windsor Act II, Scene II, Falstaff refuses to lend money to Pistol, so Pistol replies, “Why, then the world’s mine oyster, which I will open with a sword.” Even though Pistol has no money, he still has the opportunity to find wealth in the world, and uses the analogy of finding a pearl in an oyster.