Best one I know of is that saying 'on earth as it is in heaven'.
What you came to earth to learn is what your soul asked to learn.
But you can chose to go off your plan and make other choices which alter things.
If you chose to learn cooperation with others but your obstacle is avoidant personality, you are having to try harder than most people to learn that lesson. Free will and chosing not to cooperate might mean you will not get to learn cooperation for example. What Van Praagh says is follow your passion. This is how you know what your plan is by how passionate you feel about something. Synchronicity will guide you too.
For example, have you noticed how when you have a leap of faith and you are going in the right direction, everything falls into place? And obstacles will appear in areas to tell you you are off your track? Intuition helps guide you to your purpose. Free will are your actual choices. Intuition is your guide post. So now, think of what it feels like to use both. When something keeps repeating itself with relationships or situations, it might be guiding you to chose something.