Comparison. People are mostly affected by inferiority complex because of comparison and the social media age has made comparison so easy.
You see someone your age bracket and you immediately begin to compare your life with theirs. You think they are better and so you begin to feel bad about yourself.
The only person you should compare yourself with is you. Compete against you, not the world.
And as Julie suggested, comparing ourselves to others.
Or some combination of both.
Inferiority complex is something that sort of builds along the way as you grow. it is not present in all individuals but only in those that have been treated very wrongly right from childhood.
It could have been a teacher's remark that made the child feel inferior to others and when other people picked the thread, the person who was ridiculed started feeling that he/she was indeed sub par or inferior to others.
I, for one was a frail kid in childhood. There were kids in my class who were excellent in sports and almost anything they came across. When I started wearing spectacles, it made the picture complete and many started to ridicule me and say that I was inferior to them in all ways.
I knew that if I complained to my parents, my dad would report it and I did not want to tell on my friends. I just ignored it and there was nothing physical involved. I did feel though that I was not much of anything.
Ironically, fate does have the say and I went my way and my classmates went their ways. Although my life has been full of both thorns and rose petals, I try to practice the doctrine of detachment as taught in the holy BHAGAVAD GITA by Lord Krishna and it has helped me stay cool even when people ridicule me.
My late dad always told me to ignore taunts, insults and ridicule and not get involved at all because if we do start to retaliate, then there is no going back.
Remember, those who want to make trouble bait you like baiting the large fish with a small fish or worm. don't bother to catch it and you are saved.
Never feel inferior. You are special and you have your own special talents. Work on it and be successful.
Inferiority Complex is more common than we want to admit. Even sucessful people may actually owe their success to this sense of inadequacy or this desire to overcompensate for past alleged failures or weaknesses. It is very easy for a child to develop an inferiority complex and at times very difficult to overcome it, even as a grownup.
Plant in a child the idea that s/he is incompetent, worthless or not as good as others and you'll get an insecure adult who may never be able to achieve much in life or will carry that dark cloud of insecurity and resentment with him for a good part of their lives.
Inferiority complex can start at home or as soon as children start interacting with other kids in a day care, with relatives, or at school.
Whenever a child does something that is not well received by the group or worse yet, becomes the object of derision or mockery, s/he will internalize the idea that s/he is incompetent or that s/he should avoid doing that again. That's how some children avoid singing or dancing, for instance if they feel that they are not as good as others and that only excellence in such activities will provoke positive feedback.
That's why in some cultures it is so important to encourage children with applauses and positive words, even when they perform "poorly" in artistic or physical activities. Other cultures are more strict and demanding and heavy criticism or indifference will rain over those who do not perform up to pre-established standards.
As kids grow, they will face more challenges and more situations in which their talents and limitations will be evidenced and depending on their audience's reaction they will reinforce either a strong magnetic and assertive personality or a rather self-effacing one.
Sexuality is probably one of the most dramatic and important aspect of any human being and sexual awakening may be the source of most complexes. The perception of our bodies as attractive or not, and how we perform sexually (at least how that performance is perceived by the partner) may make a big difference in a person's self-esteem.
The role of friends and family is key in helping children and adults alike deal with inferiority complexes. They can be reversed as easily as they sunk in if the proper measures are taken and if the proper positive messages are sent and reinforced.