"A profound unmitigated loneliness is the only truth of life"
- R.K. Narayan

As is the wont of most of my contemplations, the seeds are first sown by observations from daily life.  Seeds, that I guess, are normally sown in anybody for that matter.  The only 'extra' help, probably, that I lend is to hang on to the moment and let it linger until loneliness comes by and waters the seeds into growing roots.  Some roots consolidate your personality, while the others just serve to entangle you into a mesh.  Yet without roots, there can never be real convictions.
Today I watched a movie, and something lingered... 

It is in the context of couples who share a genuinely deep connection - one that does not need to be awakened, all of a sudden, through clichéd anniversaries or overly hyped valentine days.  A rebellious writer Albert Camus once said 'the brotherhood of pain is infinitely more inclusive than that of well-being.'  While others were writing love stories using words like "understanding," "trust," "affection," "mutual regard," "respect," etc., Camus used "pain." 
Though a slightly extreme example, consider a typical couple who have lost a child.  The loss would have been an extremely painful experience for both the parents, without doubt, and they would have lived it every day for the rest of their life.  It is said our brains have no memory for pleasure, and that is why we desire to experience pleasure again and again.  But for pain, there is, a memory so deep that we never desire that pain ever again.  When these parents think of their lost child, they dwell on the pain, which they know is exactly the same that their partner is going through.  They may not be on congenial or cuddly terms with each other, but when they recall their pain, they always find the connection.  In this commonality of shared pain, they inevitably bond, deeper and deeper, yet unconsciously.  An outsider would never feel the pain in the same way that they do, and that is precisely why, in sharing that common pain, they create a world for themselves.  Having lived in this exclusive world, which housed only the two of them, they would never humanely be able to leave the other alone in it. Would I be wrong if I claimed that there are no instances of divorce between such couples?
People experience happiness in different ways, according to their attitudes and preferences, but pain, especially when it is intense, is experienced in the same way.  That is why happiness is always depicted as colourful, while pain is just one colour, darkness!
Good times will make you laugh, but it is only when you cry together that you find the true connection.  The pain that bonds is not just superficial disgust or despair, but one that rends the heart - a pain that is of same nature for both partners.  It has to be intense for both and for the same reason.  That is why siblings related by blood will always share a deep bond, because they will face a common pain, whether they like it or not, when they lose their biological parents.  They may not show it in their act, but the bond always remains, rooted in their soul. 
Thus, my contemplation advises: If you want to find success in love, stop looking at compatibility charts, matching horoscopes, and common tastes and hobbies.  Instead, go find a common pain, and therein lies the key to lock your relationship.