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Talk about a perfect buy-and-hold stock market. Investors who just buy stocks and do nothing have ridden a pretty much straight line to riches.

But dont let the comfort of buying and holding lull you into making a number of serious mistakes that injure returns. Even long-term investors who arent daytrading need to pay attention to some strategic blunders that can cost them in the long run.

Theres no question buying and holding has been a winning strategy in this bull market. Just look at the Standard & Poors 500 over the past five years. It has been almost a perfect escalator ride higher. Sure, there were a few bumps in 2011 and 2012, but it was best to just ignore all that.

Chart source: MSN Money

But with success breeds complacency. Eventually, the market will run into turbulence. And when it does, even if youre a long-term buy-and-hold investor, dont make the mistakes of:

* Treating individual stocks the same as indexes. If youre buying-and-holding individual stocks, you face special risks. Unlike buy-and-hold investors who buy diversified baskets of stocks like index funds youre subjected to the risk of individual companies. And you need to treat the situation much different.

Investors who bought accessory maker Coach (COH) are a great example of this reality. Yes, the stock had been a monster winner between 2009 and early 2012. But once the stock started to crack, even buy-and-hold investors needed to be ready to bail out. Buy-and-hold investors who didnt get out of Coach have seen their 130% gains dwindle to just 11% over the past five years. They would have been better off holding a broad index fund.

Professional investors tell investors who buy individual stocks to be ready to get out once the stock falls 10% or more from the price paid. If thats too much drama for you, you should join other buy-and-hold investors who instead invest in diversified baskets of stocks. This charts shows you why:

Chart source: MSN Money

* Failing to rebalance. Just the word rebalance sounds like a gymnastics maneuver. And to other buy-and-hold investors, rebalancing seems too much like meddling or trading. But just the opposite is the case, according to research from Vanguard. Rebalancing is the process of scaling back portions of your buy-and-hold portfolio that do relatively better than other parts. Its just like trimming back the green beans in your garden if they flourish so they dont overcrowd the strawberries.

A diversified investor should own key asset classes like large U.S. stocks, emerging markets, real-estate investment trusts and value stocks. When REITs do great, like they are now. its prudent to cut them back to the proper percentage of your portfolio. The power of rebalancing is powerful over time. Vanguard estimates that keeping a portfolio on target adds up to 0.35% a portfolio annually. That adds up to real money over time, as the chart below shows:

Source: Vanguard

* Keeping your out-of-date portfolio. There are lots of things you did when you were in your 20s, that you probably shouldnt be doing in your 40s, 50s or 60s. Well let you fill in the blanks. The same goes for your portfolio. If you first put together your portfolio 20 years ago to fit your needs and risk appetite then you might need to adjust now.

Its not just theory. Lets say you crafted your portfolio when you were young and risk tolerant, like IFA.coms most aggressive portfolio. The most aggressive portfolio going might be one that has 24% U.S. company stock, 40% small U.S. company stock, 5% real estate, 18% international, 11% emerging markets and 0% bonds.

Sure, youd be happy with the long-term average returns of 11.2%. And the risk would be fine, too, when you didnt have much to gamble. But now that youre 40, 50 or 60, do you really want to have a portfolio that has an outstanding chance at falling 11% in any year and a very good chance of falling 34%?

Buy-and-hold investors, too, need to know enough to tweak their portfolios over time. Can you really handle the kind of volatility this aggressive portfolio can serve up as shown in the chart below:

Source: IFA.com

* Failing to have three to six-months of cash for emergencies. Its easy to buy-and-hold if you dont need the dough now. But its when cash demands come up, even buy-and-hold investors hands get forced. The trouble, too, is that investors often can see cash needs increase at the same time the market is depressed. During a recession, for instance, an investors income might be disrupted or reduced while stocks are in a bear market. Not having enough cash might force even a buy-and-hold investor to sell. That would be regrettable as it could undo years of discipline.

Professionals suggest having at least three months of living expenses on hand in cash but preferably six months or more. Having this cash is critical for buy and hold investors so they can afford to buy and hold.

* Ignoring taxes. Buy and hold investors know they need mind fees. Avoiding commissions from rapid-fire trading stocks or incurring capital gains is a big justification for buy and hold. But that doesnt mean investors can assume thats the only leakage to be worried about.

One of the biggest hidden fees investors can deal with are taxes. Domestic stock fund lose 2 percentage points from annual returns due to taxes, Vanguard says, which cuts investors share of the markets long-term average returns by 20%.

Since buy-and-hold investors are likely to accumulate income from dividends paid, theres a good reason to mind taxes. One suggestion for buy-and-hold investors still working is to stuff bond holdings in tax-deferred accounts. That would keep the income of the high yielding instruments out of their annual income during their high earnings years, where it might be taxed at the higher ordinary income tax rate. And buy-and-hold investors who buy funds keep an eye on how much of a bite is going to pay the tax man.

Vanguard research has shown that, of all the expenses investors pay, taxes can potentially take the biggest bite out of total returns, according to a Vanguard research document titled Tax-efficient equity investing: Solutions for Maximizing After-Tax Returns.