When do we know that the market will undergo correction?

Based on what I read, it seems that you should not bother too much about when the market will correct, rather you should focus on investing for the longer term and keeping invested as long as possible. I think market corrections can only be seen on hindsight, but by then it's already too late.

Some indicators that are availible out there are Relative Strength Index (RSI) and Volatility Index (VI). RSI is a momentum oscillator, which measures the magnitude of the price movements, with a number below 30 signifying that it is oversold, and a number above 80 signifying that is overbought. The CBOE VI may help investors to view the future direction of the market, and begins to rise when investors seem to worry about the market. These indicators have worked sometimes but like the others have mentioned, I think it's quite hard to predict.

I may be wrong, but I do not think that there is a sure way of knowing when the market will undergo correction..