3 quick points
1) I don't actually need God to tell me why I must do something in order for me to do it. We do things because God commands us to. Given, many times God does tell us why we do things, which leads me to ...
2) The ends (what God predestined us for) does not happen apart from the means (our praying, or evangelizing, or any act). Calvinists don't believe in fatalism, where there's an inevitable "destiny" that happens no matter what. We believe that God uses means to accomplish His ends.
3) Rather, it seems that the Arminian, who holds to "free will" is actually more of a fatalist in a sense. To them, we make choices not God, but God has already set a final plan which cannot be overthrown.
If we affirm that our wills are free and independent of God, then either a) we can change God's plan or b) we cannot.
a) leads us to issues with immutability
b) is basically fatalism.
But what of the Calvinist? Well, we would say that since God is sovereign over even our decisions, God does not "react" to anything we do, but has planned and working through us as part of His plan. He does not react to free agents, nor does he set a destiny that happens to us independent of how we got there.
In him we have obtained an inheritance, having been predestined according to the purpose of him who works all things according to the counsel of his will