I’ll answer the question as asked, but let me first highlight what I think is the assumption underlying the question. (If what I describe doesn’t apply to you, I apologize, but this does describe so many people that the answer will still be valuable).

My guess is that you are operating under a set of assumptions that I’ll call the Big Lie.

The Big Lie goes something like this:

• Work really hard at school,
• So you can get really good grades,
• So you can go to a really good university,
• So you can get a really good job,
• At a really good company,
• Your family, friends, and potential mates will be impressed,
• And you’ll live happily ever after.

The Big Lie is based on a few supporting lies:

• Everything can be ranked against a single hierarchy. Just like it is better to finish first in your graduating class than to finish second, it’s better to go to a first tier university than second tier. It is better to go to a first tier company (where “first tier” means companies you have heard of like Google or Amazon) than second tier.
• The higher you land on this ladder, the happier you’ll be. The winners are the happiest. The runners up are still pretty happy. If you fall off the ladder completely, you’ll be miserable.
• Talented people should jump into this competition. All compete for the same things and measure themselves based on how they are stacking up.
• Since everyone “knows” what winning and losing look like, your family and friends and social status are set by how much you are “winning.”

The people behind the Big Lie are not malicious. They often have your best interests in mind and actually believe they are helping you. They are your parents who want to see their kids in a “safe” job at a prestigious company. Your teachers who want you to get good grades to create opportunities for yourself. The big companies who create great work environments so they can have their pick of people.

Now, set the Big Lie aside for a moment, and I’ll answer the question as asked, which is why people leave jobs that are at the “top” of this hierarchy.

I know lots of people who work at companies like Google and reach a day where they start daydreaming about quitting. There are as many reasons are there are people, but some pretty typical ones are:

• They don’t enjoy the politics and lack of impact at a large company and long to join a smaller one where they can more easily feel the results of their work.
• They have a great idea for their own company and want to strike out on their own and found a startup.
• They are passionate about learning a new technology or market and want to join a lesser-known company that is focused in that area.
• They have sick parents or a spouse with a job opportunity in another city. Moving to that city would be best for their family.
• They realize they won’t be young forever and want to take a year to travel the world with their fiance and have some adventures before they settle down.
• They are simply bored of working at the same company with the same people and want to try something new to add some variety to their life.

• They realize they don’t really like the technology industry and want to become a veterinarian, chef, or nonprofit leader.

For the people who know exactly why they joined BigCo in the first place, this transition is pretty graceful. If they originally chose BigCo after an honest assessment of who they are and what their career goals are, they resign as soon as it no longer meets those needs. They go onto something bigger and better (for them) and are better off for the experience and connections they made along the way.

[fortune-brightcove videoid=4324540831001]

But if they originally joined BigCo only because they believed the Big Lie, this transition can often throw them into a personal crisis:

• If they joined BigCo because of its “prestige,” the prospect of losing that credential can throw them into an identity crisis.
• If they joined BigCo because of family pressure, they dread that call to their family to explain the “failure” of walking away from a “dream job.”
• Since BigCo is the “best,” but they are still not happy, they may feel doomed to be perpetually unhappy and ungrateful that even the best wasn’t good enough for them.
• They may realize that joining BigCo was a mistake in the first place and they just wasted years of their life when they should have been a veterinarian all along.
• They may find they are unable to leave BigCo at all. They end up conflicted, paralyzed, and quiet desperation sets it.

Companies like Google (GOOG) and Facebook (FB) are amazing, but they can be disasters for people who choose them for the wrong reasons or stay too long because of inertia.

People without a firm sense of who they are, what they want, and where their interests and passions lie are vulnerable to this. They end up taking their cues from family, friends, and teachers because they don’t have an inner compass to guide them.

Every person walking this earth is different, and changes from month to month and from year to year. Once you realize there is no “best” of anything, it becomes much easier to seek out what is “best for you” and make career decisions based on your own criteria, not based on any conventional wisdom about what success looks like.

Your decisions may or may not include a Facebook or a Google, but if they do, they should for reasons that are uniquely yours.

As Steve Jobs said, “Your time is limited, so don’t waste it living someone else’s life.”

This question originally appeared on Quora: Why do people quit their jobs at dream companies like Facebook or Google?