JUST BECAUSE YOU FIT IN, DOESN'T MEAN YOU BELONG THERE
"People who fit don't seek. The seekers are those that don't fit."
― Shannon L. Alder
Fitting in is an important part of life because it has almost everything to do with turning out in life, and this is why so many people give their best in order to feel like they are part of something. However, fitting in does not always mean being part of something, as in order to be part of a whole you have to belong there.
This is why part of fitting in is rejection, and this happens because when someone does not reject a particular person then they might be rejected for not rejecting that person. Most people respond differently, some people might dress and act totally different just to try to fit in that way. Being rejected is a dismal feeling, and there is so much social pressure now that it is getting harder and harder to fit in.
From my perspective, social pressure is the most destructive aspect of the society we live in, as it influences the way we act, look, sound, walk, and so on, trying to eliminate individualization and encouraging the urge to fit in.

The need for acceptance is a basic human instinct, although some value it more than others. We all want to fit in, to belong, and in order to achieve that, we often present slightly different versions of who we are, depending on the environment and whose company we are in. We might have numerous editions of ourselves for school, work, home or even online, all tweaked and modified in order to be accepted in that particular situation. This duplicity works very well for most of us, but some people only have one version of themselves to present. They are unable, or unwilling, to sandpaper themselves down to fit society's expectations, and because their behavior or appearance doesn't quite match the herd, they are pushed further and further to the periphery of a community.
Furthermore, the most problematic aspect of this rejection is that community support is a huge protective factor in mental illness patients, and people are much more likely to remain well if they have a network of compassionate individuals around them. Isolation is a risk factor, not only for developing mental health problems but also for exacerbating preexisting conditions.
I profondly think that there is a little unbelonging in all of us, and that we spend our lives attempting to disguise it. However, I tbelieve that it would be empowering to embrace our differences, rather than fear them. For example, instead of living our lives in monochrome, it might be more fulfilling to search for the color, and the variance, in those around us, and we can then allow ourselves to be accepted for who we really are, not for the fragments of our characters we allow people to see.
Everybody tries to fit in because they desperately want to feel at home wherever they are. But fitting in will never get you home. Fitting in is about trying to adapt to a world that's not your own. You don't belong there, however, belonging is about inhabiting the world as the real you. And the hard reality is that you'll never truly fit in where you don't belong.
All in all, I think that focusing on social pressure and fitting in is the obstacle which prevents us from finding ourselves, hence only by fighting the urge to fit in we will be able to find our identities and discover where we truly belong.
"Those who are happy, belong more to themselves than they belong to the world."
― Dr Prem Jagyasi