अन्तरमुखी सदा सुखी

It is well known that one who looks inwards will always be happy.

Why is it so?

That happiness we are talking about is not just happiness, but it is ever lasting bliss, there can not be anything better than this, which is ultimate. 

This bliss is associated with owning up that Brahman, which is nothing but you. But this Brahman can not be objectified as something as Brahman is beyond human perception with sense organs. 

So when we look outwards we are getting diverted with the external worldly things & it is in the wrong direction. 

When we look inwards, your mind is not diverted, you are focusing on Brahman. This is the only way to achieve the goal.