Equanimity is the ability to remain calm under pressure. It means having an even mind, and it's a crucial factor in investing. If you can control your temperament you will greatly improve your chances of success.
If you are a mutual fund investor, you should adopt the mindset that you will make periodic investments over the long haul, and you should not pay the slightest attention to whether the market is going up or down. Your goal should be to make monthly investments through thick and thin...and especially through thin, since that's when you get to buy shares cheap.
If you are a stock investor you should see your goal is to buy shares of great companies and hold them for years. At least 5 years, and preferably 10, 20, 30 years or forever. The other approaches to so-called "investing," namely day trading, speculating on stock options - are all gambles.
Charlie Munger and his business partner, Warren Buffett, who together run Berkshire Hathaway believe that the passage of time is the friend of the investor or business person and impatience his or her enemy. When asked once about whether he was worried about a big drop in the value of Berkshire Munger said succinctly:
“Zero. This is the third time Warren and I have seen our holdings in Berkshire Hathway go down, top tick to bottom tick, by 50%. I think it’s in the nature of long term shareholding of the normal vicissitudes of worldly outcomes of markets that the long-term holder has his quoted value of his stocks go down by say 50%.
"In fact you can argue that if you’re not willing to react with equanimity to a market price decline of 50% two or three times a century you’re not fit to be a common shareholder and you deserve the mediocre result you’re going to get compared to the people who do have the temperament, who can be more philosophical about these market fluctuations.”
Stay calm despite market fluctuations and keep a calm mind. It's a key factor to your investing success.