Your investment portfolio isn't something you should simply set and forget. Rather, it's important to look at your investments every so often to make sure the stocks you own are performing as expected, and also, to make sure you're maintaining a nice, diverse mix of companies.

But while doing a quarterly investment checkup is a wise idea, checking your portfolio every day is anything but. Here are a few reasons not to log into your brokerage or retirement account on a daily basis.

Person at laptop covering eyes

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1. It's bad for your mental health

During periods of stock market volatility, your portfolio value can fluctuate substantially from one day to the next. And if you have a decent portfolio size, that could mean see you investments' value drop thousands of dollars overnight, at least on screen.

That sort of thing just isn't great for your mental health. It's demoralizing to see that a portfolio worth $210,000 one day is now being valued at $203,000 due to crazy stock market swings, so you're better off not putting yourself through that torture -- especially since it could be the case that a day or two later, your portfolio is back up to $210,000 or even higher.

2. It could lead you to make rash decisions

Seeing the value of your investments plummet on screen could drive you to make poor decisions that lead you to lose money needlessly. And the more frequently you check your portfolio, the greater the chances of that happening.

Let's revisit our example. If your portfolio declines by $7,000 in value overnight but you don't actually sell any of your stocks, you won't really lose that $7,000. But if you do go out and dump stocks, you'll turn a hypothetical loss into an actual one.

3. Day to day fluctuations shouldn't matter

Some people buy stocks with the hopes of making a quick buck. But that strategy often works out poorly.

A much better bet is to load up on quality stocks and hold them for several decades. And if you own stocks in a retirement plan, then you should definitely be taking a long-term approach in that account.

Once you get in the mindset of investing for the long haul, you should come to the realization that daily fluctuations in your portfolio don't actually mean a thing. After all, if you're 20 years away from retiring and cashing out some of your investments, then even a drastic single-day drop will be meaningless in the grand scheme of your total window -- and so checking your portfolio daily is, in that case, really just a waste of time.

Don't torture yourself

To be clear, checking up on your investments on occasion is a smart thing. It could be that there's a stock in your portfolio that's consistently been losing value since you bought it while the broad market has been doing well, and if you don't do that checkup, you won't know to take action.

But checking your portfolio every day is a silly, needless thing to do given the amount of stress it might cause you. And that's reason enough to resist that urge.