A few days into my first post-college, big-boy job with the Federal government, my boss offered me one of the most profound bits of professional advice I have ever received.

“If you want to succeed here, or in any other job,” he said, “then you have to become an expert.”

I asked the obvious question: “An expert in what, sir?”

“It doesn’t matter. Just make yourself an expert in something, and when you’ve done that, you’ll be indispensable.”

Not much for a literal-minded office neophyte to work with, but I took his words at face value and looked for a field in which I could become an expert. As it turned out, this was right around the time that the Federal government decided that fraud, waste, abuse and mismanagement were bad things, and that agencies might want to consider implementing systems to ensure their organizations were free from such burdens on the taxpayers’ wallets.

Rules and regulations for what were dubbed “internal controls” fell from on high, most of them jargon-heavy codifications of such common-sense rules as “Don’t let the fox guard the henhouse” and “A penny saved is a penny earned.” It dropped to the office where I worked to figure out how we might satisfy the District of Columbiacrats, but without fundamentally changing our agency’s own culture (which was already frugal, self-policing, and pragmatic to a fault) or wrapping our engineers in cocoons of sticky red tape and paperwork. In short, we needed an Internal Controls Expert. I saw (and took) the perfect opportunity to run with the wisdom my boss had imparted to me.

Over the years, I have parlayed my early success as that program’s nascent internal controls expert into a variety of interesting positions and opportunities. Of course, I’ve had to become an expert in many other things (budgeting, security, procurement, fundraising, public relations, historic preservation, urban forestry and arboriculture among them) in order to keep myself fresh and marketable in changing work situations. But the fundamental lesson remains valid: as long as you’re the go-to guy or gal for some necessary discipline in your professional field, you’ll always be in demand.

So how do you become an expert? First off, you’ve got to carefully pick your field of expertise. There are two optimal ways of doing this: either by picking a field that no one knows they need until you convince them otherwise, or by picking a field that everyone knows they need, but in which no one else wants to become the expert.

Once you’ve identified your field, research is the crucial next step. You should seek the most primary, core documents available, so that you can assimilate and spin them in your way and on your own terms, rather than relying on secondary spin by others. Read like a fiend. And write about what you read. And argue with your colleagues, and win those arguments. You’ve got to have a working comprehension of the field that will allow you to go several questions deep when challenged, and (perhaps most importantly) you have to possess complete mastery of the field’s lingo and jargon, so you’re not undone by an infelicitous slip in terminology at a key juncture.

Note well, though, that when faced in public with the unanswerable question or the indecipherable phrase, the true expert relies less on bluff-on-the-spot than on convincing others that he or she knows exactly where to get the right answer. It’s always better to say “I’ll find out, sir” (and then find out, fast, and right) than it is to get caught in a tortured obfuscation of some point about which you’re uncertain.

You look far more confident and in control that way, and confidence is key to becoming an expert. If you don’t believe in your expertise, then no one else will either, and if no one else believes in your expertise, then you’ve failed in making yourself indispensable. You’ve got to market your expertise, too, since if no one knows about it, then you’re not doing yourself (or your employer) any good in having it. If you say something long and loud enough, it’s more than likely to become true (or to be perceived as truth, which is essentially the same thing).

This is why every waiter in New York will tell you he’s an actor. This is why freelance writers call themselves freelance writers, even when no one is (yet) paying for their work. You’ve got to hang your shingle as soon as you can, probably before you’re really ready to do so, since you will gain more expertise by actual real-world work and interaction than you will by overstaying your time in research mode. You’ll learn from your mistakes this way, too, oftentimes more than you’ll learn from your successes.

But you will have successes and you will learn from them, as will others. Once you’ve deployed your expertise with aplomb a few times, those who benefit from it will continue to seek you out, and will generally spread the word about your expertise to others, since everyone likes to get credit for being the first to spot something or someone useful. Success and expertise snowball from this point, one feeding the other, until the day when you realize that, holy crow, you really are an expert in your chosen field, and you really have made yourself indispensable.

And what do you do then? You keep your eyes and ears open for a new field of expertise, since nobody wants to read yesterday’s news, everybody wants to know what you’ve done for them lately, and the only things constant in life are change . . . and the demand for experts to shepherd others through it.