hmm. first, i’d like to ask what you (or they) mean by being normal? i’m assuming that they mean being extraverted?
but to first answer your question, we need to understand that intro/extraversion are personality traits - detectable at an extremely young age and close to impossible to change.
secondly, we need to understand that it is NOT environment that shapes these personality traits but genetics. twin studies have shown that intro/extraversion has a strong genetic component (about 50-58%) and environment does little to affect it (e.g., most of my dad’s family are extraverts - my grandma, two out of three uncles and my aunt are extraverts but my granddad, dad and his other brother are introverts).
thirdly, no one person is 100% introverted or extraverted. imagine a continuum running from introversion to extraversion. all people lie somewhere along that continuum. i would identify myself as 70% introvert, 30% extravert. my sister is around 50/50 as she exhibits behaviours of both (ambivert). it’s just a matter of how you react to the world: extraverts are energised by the people around them; introverts are energised by being alone with their thoughts.
that being said, it would be hard for anyone to try to train themselves to be more introverted or extraverted, simply because it’s ingrained in us to act one way or another. for extraverts, they will find it hard to get any stimulation at all if you asked them to keep to themselves for long periods of time. and an introvert will always get tired of being around people and will need time away from interaction in order to go back to socialising. it will never get easier to constantly spend time around people.
unfortunately, there has been almost no research on ‘training’ one personality type into another. the only reason i can think of, of why people want to change their personality type is because we’ve been constantly bombarded by the rest of the world that extraversion is the good type - you’re much more successful, it’s easier to go about life, you’re happier (all false by the way).
no, introversion is just as good! being an introvert doesn’t mean you’re socially incapable. it’s NOT a handicap and it is definitely NOT abnormal.
i hope this answers your question in some way. :)
if you guys have anymore questions, feel free to ask!