1. You don't know what is going to happen next. Nor does anyone else.

"The fact that people will be full of greed or folly is predictable. The sequence is not predictable." -Warren Buffet

More information is NOT going to help you - Stop trying to figure out '˜Why?' You can read 100 articles and watch CNBC all day and you still wouldn't know which way the markets will go tomorrow. You would know what happened yesterday. But what will happen from here on is something that no one can tell you. No one. Understanding this is so important that I will repeat it. No one knows which way the markets will go tomorrow. No one knows if it is already over or will it go on for another 5%, 10% or 20%? No one.

2. There is NO investing or trading strategy that will not lose 20-30% periodically.

Not once or twice but periodically. Sometimes even more. No matter how frequently you trade or how much business news you consume or how many spreadsheets of analysis you have. This is just how it is. If it was not like this, investing would be risk-free and there would be no excess returns over a Fixed Deposit.

3.Selling now to buy it back later does not work.

Why? Because of 1) and 2) above.
Focus on things that you can control. Know yourself. Get a plan that you will be comfortable with during bad times and then just stick to it without worrying about the ups and downs of the stock market.