When it comes to defining your objective in life (the grandiose “life purpose”) first you must understand that there are two types of objectives in life. One is existential, and the other one is occupational.
Here’s an example: Simon Sinek, author of Start with Why, defines his existential purpose: “to inspire people to do the things that inspire them, so that together, we can change our world.” Notice how he uses broad words such as “people,” “things,” and “change the world."
Now on the other side, there is the occupational purpose that tends to be more specific. To illustrate, here’s a quick exercise by Adam Leipzig on TEDxMalibu , to define your occupational purpose.
Who are you?
What do you do?
Who do you do it for?
What those people want or need?
How did those people change or transform as a result of what you give them?
After going through answering these questions, I ended up with the following why statement (or occupational purpose) as it relates to what I do today.
I’m Alonso; and I run digital marketing programs for the owners of a small sales training company who want to achieve their revenue goals so that they can grow their business.
If this were my existential purpose, I’d feel suffocated with how specific it is. For example, if I were to change jobs, or do something different to help businesses grow, I’d technically be no longer aligned with my purpose.
That’s why I decided to call this type of purpose "occupational" as I don’t think helping companies grow their business is the grandiose reason I’m in this world. What I think is that it's just one of the skills that I’ve been given to fulfill my existential purpose.
For that reason, I’ve come to believe that living your purpose happens at different levels. On an occupational level, it merely means defining why you do what you do. And on an existential level, it means being receptive and coachable to the commands of a superior being or natural law—which I call God.
In tactical terms by "being receptive,” I mean keeping tabs on what you enjoy doing (as it relates to tasks performed to serve others) and continue to pursue doing more of those tasks as you climb different occupational ladders.
I’ve also noticed as I read many people’s existential purposes that they all pretty much say the same thing: “help others to make the world a better place.” These are usually so vague that they can apply to almost anyone’s existential purpose (think Chinese fortune cookies).
Take for example these two existential purposes (or why statements) by the instructors of the Why Discovery Course by Simon Sinek .
To propel people forward so that they can make their mark in the world. ~David Mead
To enable others to be extraordinary so that they can do extraordinary things. ~Peter Docker
Here’s another example of someone better known and with more than three decades in the self-help industry.
To inspire and empower people to live their highest vision in the context of love and joy, in harmony with the highest good of all concerned. ~Jack Canfield 
Initially having failed to separate my occupational purpose with these more grandiose existential purposes, it made me feel that my purpose was not good enough.
So if you’re seeking to live with purpose, here’s a recipe: define why you do what you do today, optimize for doing more of what you enjoy to do next, and let the specific details (the "how" and the "what") of your existential purpose unfold itself in front of you as you grow.