Looks like we are gapping down. Now the action like what you see today is coming after a long and enduring rally. So it is not a bad thing. Now the usual perma bears will be dancing in the street saying we told you so. But if you want to make money, you should not be very worried. And also if you want to make money in a market with 100 years of updrift, you should any way never follow perma bears.
Most sell offs have an intense selling phase. This last few days or few weeks. The risk is highest during such periods on existing positions depending on where your entry was. The moment the intense phase gets over, slowly you will find the 100% list blossoming again. In fact you will find very good set ups after few days of weakness.
On an individual stock if there is a catalyst, barring the intense sell off phase, you would find it will still rally. The universe narrows and you might need larger stops but there are opportunities.
On the short side you will find good opportunities in the same 100% plus universe once the market turns. Later I will talk about how using the same concept of 100% plus moves in 260 days you can build a short system. It works best when market reverses after a long rally.
Later: How to find high probability shorts