This article can be found in the MyWallSt App. Sign up today for a free account and get access to dozens of expertly written articles and analyst opinion pieces every month.

"Rule No. 1: Never lose money. Rule No. 2: Never forget rule No. 1." -- Warren Buffett

If you cracked Warren Buffett open like an egg, nothing but wisdom would spill out. Wisdom such as the line above, which is all the more important during volatile times like this.

After all, it's an easy time of year to fall prey to your trigger-happy instincts for a number of reasons:

• Stock prices are all over the place.
• Inflation is freaking everyone out.
• Supply chain issues are rampant.
• COVID is still looming like some cough-inducing specter.
• Some of your stocks are in the red...

Let's look at that last part. In times of strife, you might be looking to perform a sort of mental reset, as well looking to replenish, cut your losses, and make -- often irrational -- big decisions.

This can cause you to panic because you think your investment will never turn positive. Sure, with long-term buying and holding there will be some dips along the way that might tempt you to cut a stock loose. 

What is the biggest mistake investors make?

But, if you ask any experienced investor about the mistakes they've made in their investing career, all of them will have a regretful story about selling stock too soon. Remember, sometimes the best thing you can do is nothing.

You've heard all this before, but it is one of the most important rules of long-term investing. While it might seem counterintuitive to sit back and relax while stocks post swift and steep losses -- I'm looking at you StoneCo -- for investors with longer-term time frames, it typically pays to wait it out.

Take this crazy Bank of America stat from a 2020 study:

Looking at data going back to 1930, it was found that if an investor missed the S&P 500's 10 best days in each decade, total returns would be just 91%, strikingly below the 14,962% return for investors who held steady throughout the ups and downs.

To paraphrase:

"the best days generally follow the worst days for stocks."

In order to keep your panic selling in check, slow down and ask yourself these questions before making a decision:

1. Was I wrong? -- Sometimes you buy for the wrong reasons. Sometimes your idea doesn't work out. But if it's fundamentally still the same company you originally invested in, then there's probably no need to sell.
2. Has something changed? -- Has a leader left the company? Has the business failed to innovate and lost its sustainable competitive advantage? If there's no change, then it might be external factors like wider market conditions
3. Do I still believe in this company? -- No matter what happens, if you still believe in the business you own...don't sell. Oftentimes, the market loses faith in a company based on a poor earnings report or some temporary problem. A long-term investor should weather these storms and wait for their stock to rebound.

And remember: a stock can only go to zero, but its growth potential is limitless. It's important to keep telling yourself that as we move forward into 2022.

However, if you are having genuine concerns about whether the business you've invested in is still the same as it was when you started, perhaps you should look at our article all about the right time to sell shares.

Don't forget to sign up today for a free MyWallSt account and get access to dozens of expertly written articles.