York the Prophet

...my liege, farewell:
What will ensue hereof, there's none can tell;
But by bad courses may be understood
That their events can never fall out good.

Richard seizes the goods of John of Gaunt upon his death, even though Bolingbroke the heir is still living. These words are York's response to the King's theft.

(This is the last of of the King's great sins: first he deprived Gloucester of life without due process of law; then he deprived Bolingbroke and Mowbray of liberty without due process of law (by banishing them); and now he deprives Gaunt of his estate--again without due process of law.)

York does not claim to be a prophet, but he understands that there is a law of consequences in this world. Bad consequences follow upon wrong actions and so the consequences that will follow upon Richard's bad actions will not be good.