Your entire human experience is internal. And so is mine.
Our sense organs gather very limited information about the world--only certain types of energies are directly perceived by our eyes, our ears, our noses, tongues and skin. Our brains interpret this already limited information and turn it into memories, which consist of some remembered sensory information, but primarily of language.
We use language to make conclusions about people, places, goals, desires, dreams. And these conclusions become our identities. When people ask about us, we tell them the stories that we have already told ourselves (which we have written, albeit with help from our parents, society, and the like) about what we like and do not like, about what we do, who we are with, what our families are is like, what our life dreams are, and what we want to remain the same and what we want to be different.
And in a very important sense, none of this experience is true.
We filter and conceptualize everything we experience, and we will continue to do that for the rest of our lives. This is part of being human. This is the way that the brain works. Even in this very moment, we are likely noticing some things and ignoring others, based on how we expect the world to be.
There is nothing that we see that has not been filtered by both our sense organs and our expectations, before we even consciously realize it is there.
So if you say that you can't believe the world is so cruel or unfair, it is the very fact that you do believe that, that you expect it, that is causing you to see that world.
Not the other way around.
The first insight, then, is to see that our lives are, for the most part, an act of our own creation. And that happiness, then, has to be an inside job.