Again and again I see talented people with ideas they want to share – books they want to write, talks they want to give, businesses they want to launch – holding back because they think they "don't know enough" about their topic.

"After all," they reason, "there are real experts on this out there – and I'm not one of them." They're thinking about the people with advanced degrees and decades of deep experience working in the field.

In fact, that's just one type of expert -- "the specialist." There are three other kinds of experts that make world-changing contributions, without specialist training.

You are likely one of these four types of expert, when it comes to the work you most want to do. As you read, identify which type (or types) of expertise you could bring to the projects you are currently pursuing as well as those that you want to pursue:

1. The Survivor

You've been through something, learned a heck of a lot along the way, and now you are on fire to share what you've learned. Maybe, like best-selling author Kris Carr, you lived through cancer and want to write about your path to health. Maybe, like Jonathan Fields, you've started a few businesses and want to share insights about entrepreneurship.

"Survivors" often worry that their personal experience is not enough to earn them credibility or allow them to make a meaningful contribution, but consider these powerful strengths of this source of authority: You have an ability to move and connect with your audience that most formal experts on your topic don't have. You can provide inspiration and role-modeling– not just information. You have insider insights that will help you create a more compelling offering for your audience.

But, be careful, here's where you could get in your own way: it's easy to over-generalize from your experience to that of others. If "survivor" is your source of expertise, tell your story as powerfully as you can, and pass on your lessons learned as just that – without making claims on having the truth or the solutions for everyone. People will listen up simply because you are honestly sharing what did and didn't work for you.

2. The Cross Trainer

When an athlete cross-trains,they "train in a sport other than the one that they compete in, with a goal of improving overall performance." In our context, the "cross trainer" is the physicist who takes a look at a problem in medicine, the family therapist who writes about fixing dysfunctional teams at work. Cross trainers have deep expertise in field "x," and bring ways of thinking from field "x" to bear as they look at field "y." Business leaders Whitney Johnson and Clay Christensen each apply theories on business development to personal development. Tom Ford applied his expertise in fashion design to cinematography when he created the stunning film, A Single Man.

Cross trainers make interdisciplinary connections and drive innovation. They see the blind spots of the conventional thinking in the field they've turned their attention to.

However, if you are a cross trainer, here's where to watch out: you may miss seeing how insights from your field of expertise are not applicable to your new topic. For example, many MBAs have hindered nonprofits by assuming that all the planning tools and metrics used in a business should be applied to nonprofits to make them more efficient.

For cross-trainers, the charge is to be bold in asking provocative questions and making interdisciplinary leaps, but humble about the applicability of anything across fields. Focus on starting new conversations and prototyping cross-training-based solutions without assumptionsabout what will in fact apply across fields.

3. The Called

Then there are those people that dive into a project out of a sense of calling. They feel an inner, mysterious sense of "this work is mine to do." Jessica Jackley felt outraged that conventional charity didn't empower the poor to help themselves, and out of a persistent frustration with that status quo, and a sense of calling, began developing Kiva.org, now the world's largest microfinance platform.

The called bring many gifts to their work.  They have sustainable passion. They have vision and – perhaps most important – ardent dissatisfaction with the status quo where insiders may have become resigned.

The challenge for the called is to trust their sense of calling. That is particularly difficult when they can't find a logical reason why they're attracted to a project, or qualified for it. The called generally feel that they don't have what they need – and they aren't who they need to be – to complete their calling.

Their charge is to start anyway in whatever partial way they can. They also need to gather mentors to fill in knowledge gaps –those who support (and aren't threatened by) an outsider bringing new ideas and vision.

4. The Specialist

In our culture, this type of authority is most validated and embraced. The specialist has formal training (degrees, certifications) or lots of work experience in the area of their project. They might also achieve their specialist knowledge by conducting extensive research on their topic.

Brene Brown, a professor of Social Work spent years conducting research on shame and vulnerability and now speaks and writes widely on these topics. Dr. Harriet Lerner honed her expertise with hundreds of clients in her private psychology practice before writing her best-selling books on our emotional lives.

The pluses of this kind of expertise are many: specialists have a sense of the standard industry knowledge on their topic. They have the benefit of industry networks. Because they've seen so many examples over the years, they can tell apart the trends and the outliers.

The downside? Specialists often get stuck in inside-the-box thinking. They can also get distracted with the politics of their field or in debates about minutiae. To avoid that, specialists must talk regularly with colleagues from related but different disciplines, and seek out rebels and dissidents at the margin of their fields, listening to their perspectives with an open mind.

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Immeasurable contributions are lost because many of us think that #4 – formal training/work experience – is the only kind of legitimate authority. We usually don't hold that belief when it applies to other people – we are thrilled to read that nonfiction book based on someone's personal journey or to listen to the interesting TED talk by a cross trainer. But for ourselves? We think we don't know enough.

To be sure, specialists are extremely important. We benefit enormously from living in an age when there is so much information available, when formal education is becoming more and more accessible, and when there are people with deep, specialized knowledge. All of that is invaluable – but it is not the only kind of value.

Identify which source – or sources – of expertise you bring to your current project. Leverage its strengths. Most of all, trust that it is enough – not because it enables you to know everything, but because it enables you to make the contribution you are uniquely qualified to make.

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How about you?

How have you successfully framed your expertise?