This very difficult question has no ready answer, though no answer that denies divine sovereignty or human freedom is a valid one:
The Arminian says that man’s free acts are known in advance but not decreed.
The Open Theist says that man’s free acts are neither known in advance nor decreed.
Some Calvinists render God culpable for sin by regarding him as the constraining cause of sin.
It is better to say that freedom is not defined by the ability to do otherwise, but by the absence of constraint in a given choice. God’s decree, as such, is determinative, but it is not constraining. How God determines apart from constraint is an inscrutability.
Stand Firm! 