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"Suppose you’re just starting out as an egg farmer, and your goal is to build up a nice, profitable business. You want to build up a flock of hens so big that they are eventually producing thousands of eggs per month.
You buy your first 100 hens, and they get right to work. You allow those eggs to hatch so more hens can be born, and you also continue to buy hens from the farm supply store. Suddenly your phone rings and it’s Farmer Joe down the road. “The price of hens has just dropped by 50%! You’ve just lost five grand on those hundred hens you bought last summer!”
Is this a sensible way to think about it?
No, of course not. You’re happy that hens are cheaper, because now you can build your egg business even faster.
Stocks are just like hens. They lay eggs called “dividends”, which are real money that can either flow automatically into your checking account, or automatically reinvest itself to buy still more stocks. Some younger companies don’t pay dividends, but that doesn’t mean they aren’t making you money – they are just reinvesting their profits to grow even faster – and eventually become a Super Hen.
There’s only one time you care if one of your shares is down: on the day you sell it."
https://www.mrmoneymustache.com/2016/02/29/what-to-do-about-...
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Unless you're actively playing the markets, or close to retirement, there's nothing really to worry about.