This is a guest post from Robert Brokamp of The Motley Fool. Robert is a Certified Financial Planner and the adviser for The Motley Fool’s Rule Your Retirement service. He also has a blog, Twittering thing. Robert contributes one new article to Get Rich Slowly every two weeks.

We financial planners and financial writers love to trot out hypothetical illustrations along the lines of “If you save 20% of your income starting at age 40, you’ll be able to retire by your late 60s, assuming an 8% rate of return” — a scenario I wrote about in March. While such projections are necessary for planning for the future, the truth is that they will most definitely be wrong once the future rolls around. There are just too many unknowable variables, such as future investment returns, inflation rates, and tax rates.

However, the unknowable unknowns aren’t just limited to economic variables, as readers often remind me after I write such an article. Here’s a tale a GRS reader told in the comments section after my March post:

In 1996 I had $78,000 in retirement funds and was 32 years old (hubby was 38). Then our home was flooded because a contractor doing a city project made a mistake. While struggling with being unable to live in the house, I was diagnosed with cancer and needed surgery ([we had] no insurance). Within a year I had cashed out the $78,000 to begin rebuilding the house and pay for surgery (we recouped a very small portion of the loss from the contractor). We sold the house and walked away with $11,000 to our name. That was in 1998.

We’ve tried to get back on track, but every time I save, something happens to eat it up: chronic illness, cost of experimental medication, hurricane and tornado damage to home over three years (part not covered by insurance), and more. Life lesson for us: Continue to save because it’s the responsible thing to do. Plan for the future, but be prepared for something to get in the way of those plans.

A sad story with an important lesson: Along your road to retirement, you may encounter speed bumps, fender-benders, road blocks, and perhaps outright tragedies. While many will be unpreventable, the financial fallout can be mitigated.

In this post, we discuss the most common causes of financial derailment, and what you can do to keep your plan on course. While many of the solutions are specific to each particular risk, there’s one line of defense that will protect your financial empire regardless of the method of assault, and that is a big, fat emergency fund. You’ve heard it before, but we’ll say it again: Have three to six months’ worth of living expenses in cash, ready to be deployed when the possible becomes the present.

Illnesses and Accidents
Health problems are expensive and can impair a person’s ability to earn a paycheck. They can also force older Americans into retirement earlier than planned. Studies indicate that as many as 45% of current retirees quit work due to health problems or disability. The haleness and heartiness of a household’s breadwinner(s) aren’t the only factor; the health problems of other relatives, such as children or elderly relatives, can consume savings and impede a career.

Your defense
As the sad tale of the above GRS reader shows, being diagnosed with a serious disease while lacking health insurance can lead to financial disaster. Being properly insured is an absolute necessity. However, no insurance policy covers all procedures and all costs. Reduce the burden of out-of-pocket expenses by participating in your employer’s flexible-spending plan, if offered, which allows you to set aside money for qualified health-care expenses. The money you contribute is not subject to income or payroll taxes.

The decision to acquire disability insurance, which replaces your paycheck in case you’re unable to work, is not as clear-cut. You already have some coverage through Social Security, though the definition of disability is very stringent. You may also have coverage through your employer. If you decide to purchase disability insurance for yourself, you’ll find that it can be expensive and complicated. However, the more your job requires that you be in good physical shape (e.g., traveling, meeting with clients, holding a scalpel, violin, or other tool), the more you should consider disability insurance. Many employers, professional associations, and other groups offer group disability policies, which can be less expensive and easier to qualify for.

Finally, one of the best ways to keep health-care costs down is to be healthy. As much as 70% of health-care costs are due to lifestyle choices — eating too much, moving too little, and putting things in our mouths that smoke, impair, or bear no resemblance to anything in nature.

Job Loss
Once the boss stops sending a paycheck, either due to a layoff or company collapse, contributions to the 401(k) also stop. Depending on the person’s employment prospects, it may also be just a matter of time before debt piles up or the nest egg is cracked to cover living expenses. It’s a recipe for a delayed retirement.

But it’s not only the unemployed who find it harder to save for retirement. These days, income insecurity also takes the form of stagnant or reduced wages, while the costs of many goods and services keep rising. In many cases, the first item in the budget that gets sacrificed is contributions to the 401(k) or IRA.

Your defense
Strengthening and expanding human capital is one of the most under-appreciated concepts in financial planning. To shore up your ability to turn your talents into dollars, develop multiple skills, stay on top of the trends in your company and its industry, and become crucial to your employer or, if you’re self-employed, your customers.

Loss of a Spouse
Whether through death or divorce, the loss of a spouse can be emotionally and financially devastating. Most married household finances are built on two incomes, or one income and one spouse who does a lot of work that otherwise would cost money (e.g., raising kids). Then there’s the division of labor; it’s common for one spouse to handle all the bills or one to handle all the investing, with the other spouse being fairly ignorant of what’s going on. A death or divorce can leave a spouse on her or his own, often getting by on less income and having to assume all the financial housework.

Your defense
If the death of a spouse would lead to significant financial hardship, then that spouse should have life insurance. Also, don’t be in the dark about important aspects of financial planning; each spouse has to at least know enough to step in during an emergency. One subscriber to my newsletter (a man who handles most of the financial duties in his household) annually updates a document he calls “A Letter From Your Dead Husband,” which explains the family finances to his wife in the case of his untimely demise.

As for divorce, it’s not very romantic to plan for your marriage’s dissolution. But if your matrimony is full of acrimony, begin by protecting yourself while still being fair to your spouse. If you’re engaged, a prenuptial agreement can be a delicate topic but a good idea, especially if there are kids from previous relationships.

Natural Disaster
The tsunamis in Japan and tornadoes throughout America demonstrate that Mother Nature is a risk to everyone’s financial plan.

Your defense
Have enough homeowners or renters insurance, with an insurer that has a record of honoring legitimate claims. Inventory all your possessions, with proof of ownership for big-ticket items, so you can substantiate your claims if necessary. Keep copies in several places, including in a fireproof safe or safety deposit box, along with other valuable items so that they’ll have some extra protection from the elements (as well as thieves).

Kids
It costs $260,700 to raise a kid until age 17, according to the Department of Agriculture (because there’s little difference between a cow and a kid). And that doesn’t factor in college costs. Yes, children are their own form of natural disaster, at least when it comes to money. (Don’t get me started on the hair loss.)

Your defense
Scientists are working on a cure. In the meantime, enjoy all the non-financial benefits of reproducing or adopting. Such as an excuse to play Candyland and Chutes & Ladder, again… and again… and again.

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