Why is it exactly that you want to play the piano?
It is the most versatile of instruments, and can stand on its own without needing an ensemble. Therefore suitable for a loner like me. :-)
What makes it a MUST for you?
It isn't a must. For some years, when I didn't have access to a piano, I played a bit of guitar - I liked it for the same reason as the piano, namely that it worked perfectly well as solo instrument and is fairly versatile. Also has a very rich, mellow sound, and is actually better than a piano in being much cheaper and far more portable.
But ultimately it just wasn't as satisfying. It is far more difficult to master, while at the same time not having remotely the same quality of music written for it.
What would be the consequences if you couldn't play it?
Well, I would survive, but my life would become impoverished.
And what reward do you achieve once you learnt how to play or master piano playing?
I don't think I can claim to have mastered it. :-)
To the extent that I have, I have no idea what the reward is, except that I find it a meaningful activity.
Was there a certain past event in your life which triggered you to wanting to learn?
No, nothing that I can remember, but family legend has it that I could sing before I could talk, we had a piano in the house, my grandma could play quite beautifully, and so, when I was old enough, I took lessons for a few months. Didn't like it very much, so when the teacher moved to another town I didn't bother any further for some years. In my teens I regained my interest, but mostly just improvised my own stuff on the keyboard. Must have been torture for the neighbours.
I was an adult before I took it up again, teaching myself what I could. At one point I was quite serious about it too, but ultimately found that I have neither the interest nor the stomach nor the time to practice hours and hours per day, so now I am perfectly happy sticking to easy intermediate level pieces. One of the marvels of the piano is that even with humble intermediate level skills, you have access to a huge amount of music by some of the greatest composers in history.