When people say this, they usually assume it means that the world is at their feet and they are in a position where everything is going to work in their favour. Others say it to imply that they are “the pearl” and they are being cultivated for greatness. 

However, when these lines were spoken in Shakespeare’s ’The Merry Wives of Windsor’, the intention is actually quite different. 

In a conversation between two less-than-reputable characters, this conversation takes place: 

In other words, if Falstaff won’t give him money, Pistol will go and take it forcibly from other people. It’s about taking what one is not entitled to, and it has quite violent connotations. 

An oyster does not willingly open – it has to be forced.
An oyster does not willingly give up its pearl, which can take years to develop, and the oyster is often damaged or killed in the process of extracting the pearl. 

This is an image of violence, and not one of happy or fortunate circumstances at all.