There is only one true reason to do it and that is to move forward. 

In order to climb the ladder in life, sometimes you have to toss someone under the bus and expose a weakness in the chain.  If your story is not being told or the truth, as you see it, is not being brought to light, then throwing throwing someone under the bus might be the answer. If another person is blocking the rungs of the ladder that you are prepared to climb, then a challenge needs to be issued.  Just be prepared to suffer the consequences if you are defeated.  Gut check before you open your mouth.  

I played the trombone in school.  Chair tryouts occurred and the band director placed you where they saw fit in order from 1st chair (best) to last chair (worst).  From time to time there would be a challenge issued and someone from a lower placed chair would battle it out with another musician from a higher chair.  Sometimes the underdog won and chair positions changed.  The loser was usually embarrassed.  If they are competitive they would practice, get better and return the favor to the person who defeated them.  This is not retaliation.  This is growth.  Know the difference!

Why would your career be any different?  School is the place you get educated, right?  School is what sets you in motion for the rest of your life.  If you are reading this and thinking that challenging someones abilities is a terrible thing-then what did you learn in school?  Does your industry get better because nobody challenges the next guy on the ladder?  Are you more efficient because you are pacified and content with the way things are going while the rest of the world is changing?  Isn't life and career about being the best or better at something?  (Did I just write almost a whole paragraph in question marks?)

I'm not a bad guy.  I'm just keeping it real.  

I'm not talking about retaliation.  That's something completely different and comes from a shallow and weak place and not derived from honesty or growth.  Retaliation is almost always seen for what it is and eventually exposed.  Anyone can have a chip in their shoulder because of something someone else did to them (or they perceived was done to them) but is retaliation as sweet as besting someone based on a foundation of personal betterment?  Revenge is not as sweet as it is made out to be.  Not even close.

Sometimes people are telling the wrong story about you and perception becomes reality.  "Perception is reality" is a phrase that's been used for decades and it holds a lot of meaning for those who are complacent and not seeking the truth.  If you are perceived as something you are not by your peers, then two things are happening .  1) Your peers are content with the knowledge they have and 2) you are not telling the story you want told.  The person telling the story is looking for excuses as much as the person that is willing to hear them.  

If you want to BE the best, you gotta BEAT the best!  (Insert my wrestling theme music here)

Fighters climb up the ranks.  Presidents and CEOs of companies climb the ladder.  Middle managers and quarterbacks had to start somewhere. They had to best someone out of a job.  You can give yourself fancy titles all day, but actually earning the respect that comes with that title takes dedication.  Not only do others need to believe you are capable, but In order to prove that you are worthy of the title or placement, you often have to challenge someone you perceive to be weaker than you.  If they are in fact weaker, then they don't necessarily belong in the position.  If you don't bounce them out, someone else will.  If you stop learning, growing and moving forward, then someone else is prepared to do the same to you.