When I've had a rough day or few days, I sometimes remember this song from my teenage years, and the lyrics stay true to me.  I feel better in just remembering that things will get better and everything happens for a reason.  We can't always explain what happens in life but we can learn to deal and try again tomorrow.

MxPx
Tomorrow's another day

I don't want to let my life fly by
Do you ever stop, stop to wonder why?

And time flies by
When everything is ok
It just turns out that life ain't that way
Big decisions overwhelm me and I know
nothing's free

When I don't think of, think about much
People die and we don't know why
I could use some understanding
Human contact, sign that contract

I don't want to let my life fly by
Did you ever stop to wonder why-ever stop to
wonder, wonder why?

And time stands still when no one understands you
When you don't quite understand yourself
But just know this that God is faithful
Even if you don't have faith yourself

There's nothing quite like being sure of
What's inside your heart
It's mostly simple but not so easy
To know just where to start

Today didn't have to be this way
Tomorrow is another day
Another chance to make things right
A chance to make sense of last night

A chance to fully live your life
I don't want to, I don't want to, you don't want to