Most prophecies are not passive, in that they don’t come to pass regardless; they are based on what God saw in us and said we would become. Other prophecies are fulfilled without our participation (for example, the one which stated that in his death the bones of Jesus would not be broken.
Prophecy speaks to our potential. Jesus chose to die on the Cross, but he agonized over the choice in the Garden of Gethsemane. Personal prophecies will not prevent us from agonizing over tough choices and necessary decisions.
At such times they are very encouraging. Jesus knew the prophecies that predicted his sufferings and death, and knowing them helped him to submit to the will of his Father. Likewise, the Apostle Paul encouraged Timothy to “war” according to the personal prophecies spoken over him.
Those prophecies had spoken of his godly potential (1 Timothy 1:18). Yet, like Jesus, he still needed to “fight the good fight” if he was to realise that potential, and we need to do the same. God assures us that we can — we just need to assure ourselves that with His help and by His grace we will.