"If our lives are preordained, there is no reason to make an effort at anything. Because it would happen (or not happen) anyway.
Trouble is, if I decide to do nothing today, nothing will happen here."
I think you may have missed the point.
If our lives are preordained, then whether you "decide" make an effort or not, or do nothing or do something etc ... has already been preordained.
As mentioned, your belief that you have made a "decision" is merely an illusion.
I could add "so don't worry" but that has already been decided anyway !
BTW I'm not saying such is the case, but it must flow on from the belief that God is all knowing, all seeing for all time.
