Are we really predestined to practice a single career all through our lives?
Tabular Rasa: The notion that the mind at birth is an empty slate, and that it is eventually filled with the education and nuture of the individual.
The last 100 years of our human existence has presented a complex nexus of opportunity and experiences for us. With so much information to take in and/or harness, our lives can easily become frustrating in terms of making choices.
I had the experience of a well groomed Nigerian growing up: good grades, manners, and the rest. Looking back now, i can say i was always interested in learning stuff (not just school related). At the period around which i got into uni to study engineering, a thought came into my mind to do something different, and so i decided to learn the guitar to the best level i could.
The first year was difficult and i sucked, but with perseverance(i would practice for 3-4 hours a day in uni), exposure, using others' knowledge, down the years i can now play some really cool stuff.
Taking that decision, i now have something i can do till i'm literally in my 80's or more.
Also, from going away from my classroom approach to life, i have also discovered "how to learn anything", and that anyone can really do anything if the heart is set to it.
Learning anything could be stepped through:
-Having an in-depth knowledge of the fundamental concepts of the field.
-Immersing yourself in an environment where you are pushed to perform consistently(This is especially true for learning a language: i bet if you migrated to Mallorca today, your fluency in Spanish would shoot-up in three years.
-Sticking through the immediate failures
-Learning to fail and trying again and again.

This brings us to the idea of passion, or the follow your passion cliche. This school of thought postulates that EVERYONE has a natural inclination for a certain activity, and that they are to follow this activity during their time in this world. Going to the beginning of this write up, you may find that this notion is inherently flawed. This is because you cannot be inclined to what you have never been exposed to. If you only ever had chicken, you'd never say hotdogs were the best.
Rather, i say this is an era where we have to re-invent ourselves several times over the course of our lives. With several options to choose from in a speedily evolving world, in which resources are strained, this seems to be viable.
If your are in your early 20's, you could split a year of your life into six-month periods, to learn things which you think you might like. You may just fill a valuable need this way.
Passion comes in after the hard work put in to become exceptional at something valuable, not before.