You not only have to prove that you have talent and abilities, but you also have to demonstrate you have the desire and fortitude to do what it takes to deliver your value.

This becomes evident during the interview process.  I speak to job candidates all the time that are interviewing for jobs where they sincerely feel overqualified, but because they have been unexpectedly laid off, they are willing to take a lower level position for the time being.  They feel they will get the job and work until they find a better one.  The candidate will go on the interview and clearly articulate how he or she is qualified, but ultimately not be offered the job.  Then the candidate wonders what happened.  He or she certainly has the skill set to perform the job, and the interview went well, so the candidate ends up confused.

The problem is that the company knows the candidate doesn’t have the desire to stay long term in a role where they feel overqualified.  The interviewer sees all the candidates and tend to prefer the ones that are qualified and most enthusiastic about the opportunity.  It is only natural to feel more excited if you are interviewing for a job where you are getting a 20% increase from your last job, rather than the person that is getting a 20% decrease from their last job.  It may not be a fair assessment but it happens all of the time.

Demonstrating your potential is more than showing your credentials, it is also about showing desire, enthusiasm, and determination.  Your perceived long-term commitment is part of considering your potential.