I think that what has been decided will cause a major change in lifestyle is the most difficult decision because it is something that can tell the future of my life will be better or worse.
I think the decision will cause a big change in your life is the most difficult because it is something that can tell the future, my life is better or worse.
I think that what decided to make a big change in the life what is the most ตัดสินใจยาก because it is what can be said in the future, my life will be good or bad.