I have been wondering about karma/written/predestined destiny myself for quite a time..
off topic- this is jyotish forum but nevertheless, as I have been reading about Western Astrology for a couple of years, and only last year found out the impact of Hellenistic/renaissance, traditional, medieval astrology, I have become very depressed by their teaching/belief...the only thing we can do is cook soup...in the sense nothing really depends on us, if it is written, it is written, and it us up to us to choose between God and evil, and the real domain up to which we can reach is - cooking soup, both literally and metaphorically.
This has led me to really think what is that which we can change? In my opinion nothing. As you have mentioned if it was written for a person to be saved by someone, then it is only the right person at the right time in the right place...again predestined and ours is either not to know it or if we somehow know can not change it.
This is where I get depressed in the sense, no matter what I think (even though thinking again may be predestined in the sense of having an aim/ the aim is predestined to be fulfilled, so the process of thinking is alarmed and triggered by the event that is predestined as an aim to be fulfilled) but mind this, so if no matter what I think, do, feel, wish, want, hope for, fear of...the event/tragedy/happy event will happen...meaning that if one is to have a child...he/she will have it...wishing not wishing, thinking of it/not thinking of it...or again take any other event in life...if it is to happen not much actually depends on us...
And this makes me mad I must admit it...I can't change the world, the people, the circumstances, the feelings, the situations, the existence of anything actually...no matter how much energy I put...and what is the point then?
Astrology as a predictive divination science can be of help of course if precise things are predicted by serious astrologers...and maybe help us prepare for the time to come...but are we really so helpless?