Your Best Employee Is Your Weakest Link If the slacker everybody has learned to work around quits, no problem. It's the person who always picks up the slack you can't afford to lose.

The last time I used my go-to, standard illustration about the need for documentation and cross training I was doing a series of custom workshops for a medical management team.

"What if, heaven forbid," I asked them, "one of you got hit by a bus tomorrow and didn't come to work? How much would it cost the business?''

Usually when I deliver that line I see awareness dawning and heads nodding as the implications sink in, but that morning the faces staring back at me wore expressions of horror and even anger.

I soon learned that only a few months before I was hired to revamp their systems and coach individuals on the team, their office manager and her father had been killed in a car accident. This wasn't a theoretical illustration for this audience. They'd lived it.

More than that, they were a classic example of the real "weakest link" in any small business. With their office manager gone they started to discover all the tasks they took for granted in the course of a day that no one else knew how to do.

When I ask business owners and managers to identify their weakest link most of them will start a mental inventory of their team's attitude and skills. But in almost every case the weakest link isn't the slacker, or the prima donna or the dim bulb who is costing the business the most. Even without a tragic wake-up call, the weakest link is nearly always the person who knows how to do things no one else in the business can do. If that link breaks, even for a sick day or short vacation, it costs your business in small, but cumulative ways that you might not even notice. If they are able, or unwilling, to return to work those costs will accumulate fast.

Related: Key Person Insurance

The entrepreneur at a small business with only one or two employees typically has done most of the employees' tasks at some time and could still muddle through them, if necessary. But think of the cost of having what should be your most highly skilled (and compensated) person (that would be you) doing mundane but vital tasks. As you grow there will be tasks that you've hired someone to do just so you don't ever have to know how to do them. That's great, but make documentation and training part of the job description.

If you have employees who are highly specialized, documentation is even more essential because it's unlikely that their knowledge and skills are duplicated in the organization. Who hasn't heard the horror stories of the tech start up whose engineer quit and left only sloppy records of their work on the project?

If you have one trusted "right hand" person who is the only one who knows everything from the password to your online banking to where the bodies are buried, your weakest link is also enough rope for you to hang yourself with if that one trusted right hand turns out not to be trustworthy.

Related: 4 Steps to Take When a Key Employee Quits

Regardless of the type of business you're in, how large or how small, a Key Person Audit is a smart item to add to your 2016 planning agenda. Identify the weak links and create a plan for documentation, cross-training where appropriate, and even a hiring strategy if you should need to replace a key person in your organization.

I hope you never lose an employee to tragedy, or to a betrayal of trust, but life has a way of throwing us curve balls. The old parental standby is a good admonition for entrepreneurs as well. "Better safe than sorry" is a wise approach to evaluating and guarding against the day when your go-to person isn't there to go to.

Related: Having Problems With a Key Employee? Remember: No One Is Irreplaceable.