The Holy Grail is the chalice used to collect the blood from Jesus while nailed to the cross and supposedly has the power to grant everlasting life to any and all who drink from it. Its most famous searchers are the mythical King Arthur and his court. In recent years, "holy grail" has come to mean a product (usually makeup) that changes one's life for the better. You can't live without it. It gives you life every time you use it. You will always repurchase it and if the product is ever discontinued you spend an abhorrent amount of money buying as many backups as you can before diving head first into a deep depression after which you spend years looking for an acceptable replacement.