I've been hearing this for years too - "God has a plan for you/this might not be God's will for you". And I used to feel fearful in case I missed his will or messed up his plan for my life.
But while I believe that God can call us to anything he pleases, and it might be that he calls us to live in certain places or go to a certain church, I don't believe that God has a detailed plan for us and we mess things up if we don't discover and follow it.
I'm not certain that God minds too much whether we choose to become a scientist in a lab or a science teacher, an engineer or a plumber, a teacher or a nurse - I think the important thing is that we belong to him, live for him, be salt and light in the communities that we find ourselves and glorify him by using the gifts that he has given to us and by being the people he has called us to be.
Because some people choose not to know, obey, or even think about God -some feel they just don't need/want him.
I don't think hell was designed for humans - I think that God wants all those whom he created in his image, to know him.
If God wanted to "control" us at all I think he would have made us like robots, to always worship and love God, never to sin and obey him because we were programmed in that way and could do nothing else.
I had M.E for 18 years.
I don't believe it was sent by God, nor do I believe that I was "destined" to get it. I don't think it was even "chance" that I got it and not my brothers. It was no one's fault, but there were a number of contributing factors - suspected glandular fever as a child, a weakened immune system, a stressful job and series of events.
I believe strongly that God was at work during that time - he didn't send it to teach me stuff or as a punishment, but I learned a lot through it, and what it meant to trust him for strength. I also believe that he answered prayer and healed me, literally overnight, from it.