There is none.
We all theorize. Every time you stare into the ocean, or at the moon, or at the caramel sands in the blazing desert, you begin pondering about life, its meaning and therefore about its futility. The greatness of the view makes you feel like a rather insignificant speck in the grand scheme of things, and thus initiates such a thought-process which, quite obviously, has no meaningful end. But we dutifully go through this painful realization every time we sit alone in front of nature's magnificent might. And every time, we have a new theory about life.
My theory begins with Tetris. It all began three days ago when I was playing the wonderful game, resplendent in black and white. That was when it first struck me how similar it was to life itself! Blocks of different shapes and sizes were raining upon me with the spontaneity of the immense drops in a thunderstorm. They fell with such randomness that they were entirely indistinguishable from the stochastic events - opportunities and worries - that Life throws at us. You can't obviate or avoid them; you can only arrange them, try to absorb them.
As the 'Z's, the 'L's and the 'I's fell upon me, I could but divert them towards the different corners of the little screen I looked at, with the hope of achieving something spectacular - an order in a chaotic universe, which would be so beautiful that I couldn't ever take my eyes off it.
The 'Z's snuggled cozily with the 'L's, even as the spectacular 'Is's occupied those elusive voids which have always been left incomplete. And then I saw the beautiful pattern being completed. There were no voids. No spaces. No white places which required reason. The completed pattern imprinted itself in my mind in a way, I knew, I could never be freed of the haunting memory. The thought of the pattern gives me goosebumps even now - when I'm almost entirely sure that I will never again be able to replicate such splendor. Magnificent in its magic, Life is. Much like Tetris.
And then, I witnessed the greatest climax ever possible when the pattern satiated itself and collapsed. It disappeared! And it left no trace. The experience was complete, and now it was absent. It was but a memory, and therefore it was perfect. Experiences, after all, are only as perfect as the memories they are capable of creating. And it was apparent to me that day. There are no goals in life. There are never any! There are only roads which we imagine are ways to a destination. But ever so often, these roads are so romantic themselves, that you must forget the destination! Just like Tetris.
Rules of Tetris: When you make a perfect line, it disappears and all the blocks shift accordingly, leaving only a void on your screen. If you let the blocks reach the top of the Tetris board, you lose. You cannot win a Tetris game, though you can attempt to get the high score.
The point of Life isn't to reach the top, is it? The objective is to make patterns more beautiful than you can imagine, until they complete themselves and remain only as memories - memories that you want to relive. But sometimes, they come back! And we all wish that, one day, we will have the opportunity to recreate those spectacular designs.
It's the same thing with Tetris. You can't win Tetris; you only get to make a high-score. A score so high no one else can match!