I don't think it is. I reckon you should first of all write about what you ENJOY. Write about what you are enthusiastic about and would like to read about yourself. All the information you need to KNOW can be found with research. The library, your own bookshelf, the Internet (if you're careful).
Get a handle on what gives you a lift first. Think about a subject that satisfies you and gives you pleasure to think about. Then find an angle or an aspect of the subject that you haven't read about or that you personally would like to know the answer to. Then get writing.
You should also ask yourself this question: "Do I want to write for fun or do I want to write for funds?"
If you say 'funds' then you need to make sure there is a market for what you want to write. Go to references such as the Writers and Artists Yearbook in the UK - every library has one - and spend some time looking at the magazine section. Having found a magazine that looks promising, drop the editor a line, or an email, with your idea and ask if they are interested. Don't be put off by a negative response, just give a mental shrug, take it on the chin and move on to the next magazine. If you continue to draw a blank, then maybe your idea is, shall we say, ahead of its time? Back to the drawing board, then, and work on something else.
If you're writing for fun, that's great. Keep doing it. Choose a subject that you love and write about it. Whether it's fiction or non-fiction, write something to please yourself. You can always take it to your local writers circle and share it there. Then one day you'll have something that suddenly hits you and you'll say, "Hey! This is really good!" That's when you should start thinking about writing for funds!
Finally, remember the ten-minute rule. Every day sit down for just ten minutes and write something. And write about what you enjoy.