Happiness happens when we know or sense that we possess some good.

If that good is a mere temporal pleasure, then happiness is fleeting and fragile.

We then whip saw around between being a little bit happy and sad.

When we know that we are partaking in the very life of the Trinity (the greatest good imaginable), then we have far greater happiness. 

That's why saints are happy people, filled with joy.

Avoiding pains at all costs, is actually a "distancing" we try to do from God. 

Pain is part of life, a reality.   We need to stop running from pain, and instead face pain as one more way that we can live unity with Jesus Christ.