If you're like most Americans, retirement is a goal that you strive for with each paycheck you earn. You might have set up a 401(k) retirement plan through your employer, contributed to an IRA, opened up a brokerage account or done some combination of the three. You know that having a long-term outlook is the key to success when it comes to saving for retirement; however, what you might not realize is that your portfolio needs to be maintained on a regular basis in order to plan for a safe and financially healthy future.

Related: 10 Huge Mistakes to Avoid In Your Retirement Planning

Why you can't just "set and forget" your retirement savings
The old adage "set it and forget it" doesn't hold true in retirement planning anymore. It used to be that retirement was as simple as investing a monthly amount into a qualified retirement plan and letting it build up over the course of your career. Unfortunately, things have changed over the last decade or so, thanks to the tech bubble burst and financial crisis of 2008.

You need to diversify your investments
While the idea of investing for the long term is sound, another key element must be added to make the strategy viable: diversification.

Diversification is the financial equivalent of "not putting all your eggs in one basket." The idea is to hold a mixture of investments -- stocks, bonds, real estate, currency, cash and other financial instruments -- in your portfolio.

You might think that you want to optimize your assets; you're trying to save for retirement, a lofty goal that's going to require a large amount of money -- why not just put all your money into stocks and hold on through the ups and downs?

The simple answer is there's always some kind of bubble or crisis that occurs in the stock market -- the tech bubble of the 2000s and the more recent subprime mortgage crisis in 2008, for example. Imagine if your retirement was scheduled to happen in one of those years. You might have to keep working for a long time to recoup those losses.

Related: 3 Ways to Salvage Your Retirement Plan If You Haven’t Saved

You need to rebalance your portfolio regularly
So you understand about diversification and you invest in a portfolio that includes a good balance of stocks, bonds and other asset classes. Now you can sit back and relax, right?

Wrong. Over time, your investment portfolio will become unbalanced. Stocks generally appreciate at a faster rate than bonds and, left unchecked, stocks can quickly become the largest asset class you own by a wide margin.

You should check your retirement portfolio on a regular basis and make adjustments if it's misaligned by 10% or more. A little deviation is OK, but you want to keep large mismatches in check.

How often is too often to check in on your portfolio?
Keep in mind, moderation is the key to maintaining a good balance. Too much readjusting can lead to problems as well.

The first problem with too much interference is the possibility of missing out on gains. If your stock holdings begin to rise faster than your bonds, don't start reallocating immediately. You should take advantage of the increase until it becomes too unbalanced -- again, 10% or more.

The other major issue is that you will essentially be hamstringing yourself by constantly changing your portfolio. If you have a brokerage account and you're trading stocks, you'll incur a transaction fee every time you buy and sell an investment. Too many changes will rack up the fees and take away from any gains you might have realized.

Mutual funds can be especially dangerous to adjust. Some types of mutual funds have share classes that come with a sales charge in exchange for low internal management fees. Over time, these funds tend to generate better returns than the fund classes with no sales charge and higher internal fees. Selling those shares early before you've recouped your upfront costs can greatly affect your long-term performance.

The best way to approach your retirement portfolio is to check it on a quarterly basis. Unless the market has a long period of appreciation or depreciation, you shouldn't have to make changes more than once a year to once every couple years.

Setting up a retirement account isn't a quick fix that results in success. Proper management of your assets will ensure that you don't miss out on opportunities while making the most out of the investments you own.

This article originally appeared on Go Banking Rates.