You're a team player; nothing great has ever been accomplished with just one person. Anyone who says otherwise is probably a not very nice person, and not someone who you feel the need to be associated with. You make friends for life, and you take those relationships very seriously. Like, blood oath seriously.
There is nothing that has been invented that we cannot live without. Because, for something to be invented we've had to not have had it before. People sure would piss and moan though if the car was taken away....to answer your question.
People with preexisting conditions will have a harder time adapting to the lack of an organ. Your chances of adapting go down as you age as well. As to why could someone live without any of these organs, you'd have to know how the organs work, and how can the body adapt to the lack of them.