Let me take my own example. I strongly believe that ‘the accident’ was inevitable- perhaps it would have happened differently in a many-universes interpretation (quantum mechanics), but it was bound to happen. So I do not go into the “what-if” mode, with a sad look on the face every now and then. However, everything that happened after that was a factor of conscious choices that I had made.
Everything cannot be predestined, since that removes the human experience (and choice) entirely out of the equation, and everything would be programmed by the one above. Everything can’t be up to ‘free will’, since that makes the equation very unstable (with only variables), and people will then go into an endless loop of the “What-if” syndrome.
We always have a choice- the choice to do what is right (disclaimer-definition of ‘right’ is subjective). Events in life are essentially the sum of these choices that we make. In hindsight, we might realize that some of these choices weren’t really choices, and that thing was predestined; but that’s a small number. So that’s that on the topic. Yes, some milestones in life are predestined and already carved into the road, but it’s up to you to ensure that the road ‘as such’ continues to remain smooth and not patchy, through the journey.