Charlie Munger
Lacy O’Toole | CNBC

Avoiding mistakes in business and life comes down a few simple things, according to billionaire investor Charlie Munger, who died last week at age 99: good financial habits, integrity and “avoiding toxic people and toxic activities.”

Munger shared the advice during a Q&A session at Berkshire Hathaway’s annual shareholders meeting in May.

An investing icon in his own right, Munger was the long-time business partner of Warren Buffett, the enormously successful investor and CEO of Berkshire Hathaway.

For decades, shareholders have flocked to the company’s annual meeting just to hear Buffett and Munger’s advice.

People are “almost certain to succeed” if they spend less than they earn, invest shrewdly, learn continually and remain disciplined, Munger continued.

Without those traits, you’ll need a lot of luck to be successful, he said.

As for avoiding toxic people, look out for those “who are trying to fool you or lie to you or aren’t reliable in meeting their commitments,” Munger said.

“A great lesson of life is get them the hell out of your life — and do it fast.”

Munger’s advice echoes comments he made in 2019 to CNBC’s Becky Quick about living a “long and happy life.”

The secret to a happy life is being cheerful despite your troubles, and avoiding traits commonly associated with toxic people, like envy or resentment, Munger said.

As a rule, you should “deal with reliable people, and you do what you’re supposed to do.”

“All these simple rules work so well to make your life better.

And they’re so trite,” Munger said in 2019.

At the shareholders meeting in May, Buffett shared his own thoughts on the topic.

To him, most major mistakes in life can be avoided by simply being a good person who acts with integrity.

In making his point, Buffett recalled advice he received from his longtime friend and business partner Tom Murphy: “You can always tell someone to go to hell tomorrow.”

“Think about what great advice it is when you sit down at a computer and screw your life up forever by telling someone to go to hell, or something else, in 30 seconds and you can’t erase it,” Buffett said.

In other words, think twice about giving someone a piece of your mind.

As tempting as it may be in the moment, it’s likely not worth the long-term risk to your reputation.

After all, how you treat others is a reflection of your own values.

“Write your obituary and figure out how to live up to it,” he said, adding that he’s never known a kind person who “died without friends.”