Even though all the above reasons do apply the best reason of all is it gives a chance for you to do it for yourself.
If you are thinking: Why on earth would I want to start doing work? How does this benefit me personally?
First of all, you get to try experiencing the career of your choice. You can find out what you enjoy or don't enjoy and utilize that knowledge to find more suitable future jobs.
Secondly, you are allowing yourself to try new things. Some things can only be truly learned from the hands-on application.
The third is the network you build for yourself with the new friends, colleagues, and acquaintances you meet. Personal development does not always happen in isolation.
Lastly is the satisfaction you get from improving yourself. In the end, you should feel a sense of personal accomplishment from what you've achieved.