The OPI bar, when it is green, indicates at least 2 of the charting indicators are showing positive signals. You can see these signal in your portfolio.

And on the chart

Closer inspection of the chart above shows that the MACD is decreasing and the Stochastic has already dropped below the 70% line. If the price drops at the end of today's trading, the OPI bar is likely to be bearish tomorrow.

Advance the calendar forward 1 day and you will notice this has occurred.

The price had trended up but has started to reverse. This forced the MACD and Stochastic to give bearish signals. Selling under these conditions is similar to an insurance policy. You insure your life, your home, even the clothes on your back. Then why not insure your investments as well? If the share price begins a significant decline, then you have sold out before that loss and preserved your capital. If you are wrong about the price going down, then it is a simple process of buying the stock back to profit from the next rise.