What Does It Take To Forget?

I guess its easy to live life somewhat with positivity without looking back and moving forward
but is it easy to remove certain things from our memories  altogether? I suppose that's a stupid question to ask but I still wonder

how many of us can forget things and also remove them from our unconscious mind?
Is it even possible to do so?

I don't really know much about spirituality or however these things works

But when we have long forgotten things in our lives, why do they still haunt us in our dreams?

The tears which we never shed when the painful incident occurred

Why do they fall in the dreams so uncontrollably?
Why is it that it feel like we have no pain and our feelings all cold and we are living our life happily and positively
Yet in our dreams it hurts so much that you cant breathe?

I keep telling everyone that its pointless running after something which you know you cant have
So why do we still do that?
Why cant we just grasp the Happiness which is right ahead of us?
Why does this unconscious mind takes over and makes us stagger around the negative path when we aren't even aware of it?

Lol
This might be my first most confusing post ever for certain people
who are just as clueless as i am when it comes to these things xD