I've never had the greatest self esteem or self confidence. I don't consider myself above average. However, I would find it incredibly hard to believe that any one person can be above average in everything. My husband is above average in Math, terrible at English.... I am above average in English, horrible at Math.
I've always thought of myself as a girl-next-door, plain Jane type.... And yet, I've had plenty of guys tell me I'm far above that... One even went as far as to call me a Goddess.....And I still look in the mirror and just see an average person.
When it comes to my job I know there are things that I really excel at... And things I put off because I don't want to deal with it because it frustrates me... So overall, I'm above-average at some things... But I'm still pretty much a Jack of all trades, master of none.... And I've learned to accept it and appreciate it.
We all tend to also excel at what's important to ourselves, or consider important what we just happen to be good at. If a large amount of your self worth is being a gardener, there's a good chance that you've put in enough effort to above average at that, which makes you feel above average.
I used to think that I was stupid and slow in primary through secondary school because my teachers were constantly telling me that. They were also constantly on my back for not paying attention and not doing homework that I felt had no point e.g. copying essays straight out of a book and practicing math.
Then I took an IQ test and I realised that it simply wasn't true. I am just easily bored. Now I'm doing a PhD and am tired of everyone around me constantly telling me that I'm smart/clever because I don't feel it, in the least.
Sometimes I think about how my teachers would respond if I went back to school to visit them (especially those who called me stupid/slow and hit me) and waved my PhD in their non-degree-holding faces. But I don't care enough about that to actually do it.
The people below average are not 50%, because most people are average (or close to average)...so there will be 3 categories, below average, average, and above average.
Now...assuming that 30% of the inhabitants of Earth are pretty dumb, what are the actual odds of them thinking that they are dumb?! Remember Forrest Gump? (He's a fictive character but a good example anyway) He could play ping pong. He was actually pretty good at it. Now is it not possible that being good at something would make a so called dumb person to think they're above average? Actually seeing that you beat 95% of the people you play ping pong with would make you feel above average right? Even though you suck at abstract thinking or whatever.
Most people have something they're good at, they' have a hobby/activity where they're above average, so they may generalize that they're above average overall. Generalization is not that uncommon isn't it?
Although people may also think they're above average because they feel like it...most dumb people I met do not think they're dumb, they actually interpret their dumbness as being a sign of intelligence. How do you do that? By thinking/saying things that don't make sense.
Realize that 100% of people could overestimate their abilities. If you think you are the best person in the world at something but are really 98 percentile you over estimated but you are hardly below average. The fastest runner in the world could think they can do better and overestimate themselves. Simply because someone is above average does not mean they can't overestimate their abilities.
Ne > Ti > Si >> Te > Se >> Fe > Fi > Ni