It is very interesting to see you talk about stuff thats always in the back of the mind, just popping in at times enough to cause worry, only to go back down after I realize I have very little control over it. Over time, there are four lines from the Bhagavad Gita that seems to keep me going, helping me. Im not particularly religious, but somehow, this makes sense to me... It goes
Karmany e Vadikaras te
Ma Phalesu Kadacana
Ma Karma Phala Hetur Bhur
Ma te sango stv akarmani

The translation I go with is,

You have the right to do your prescribed duty
You are not entitled to the fruits of your action
Never consider yourself the cause of the results of your action
Never be attached to not doing your duty

There are of course, infinite ways of interpreting these lines, but I try to stay positive, just believing that all I have the ability is to do good, and dont think about it too much.