Don't think you have to know everything. It takes years to understand investing, and no one fully knows exactly what's happening all the time. You will make investment decisions with as many facts as you can assemble but you have to realize that you can never really know everything. One of the secrets to investing is learning your own trading method(s) that work for you. More knowledge about stock markets can only make you wiser and richer! Real learning occurs through repetition, making mistakes, identifying them and devising strategies to improve in future.
When you are starting to invest, it is best to start small and take the risks with money you are prepared to lose. As you gain confidence and become more adept at evaluating stocks and reading the market sentiment, you can start making bigger investments. The trick is learning to invest in more stable stocks before you jump into other stocks.
No matter how much you think you're prepared, stock market will always keep you on your toes and hit you with something unexpected. YOU have to try it for yourself. Don't judge it by looking at it or even hearing what people say about it!! LEARN FROM THE REAL EXPERIENCE!!
Even after learning all the trading principles there comes a time when you end up making a massive loss for whatever cause. It is thus important to learn to cope with such a scenario. For a new trader who had never experienced a massive loss, it would definitely be hard to stomach.
Stock market is like roller coasters; they have Ups and Downs, Twists and Turns, and you never know what Speed you'll be going at any point in time. You'll never know what's coming...a Drop, a Loop, a Hard Turn, or maybe a Climb to the top of a Steep Hill.... So be prepared for anything that happens.