People are born with an innate personality, given that big 5 is highly heritable (h2 = 60-90%) when peer-reports are assessed instead of self-reports. However, I think that people can also alter their behaviour depending on their given environment and beliefs. For example, humans have gotten more extroverted during the last 100-150 years or so [1] [2], presumably due to increased urbanization/traveling and public schooling. In addition, personality appears to change with age, though I assume that some of this is due to changes in goals (e.g. younger people are more concerned with status, older people more concerned with peers).
However, I think that a human’s behaviour can only be altered up to a point by what I call factor C. If an individual has a C of 2, they could increase their conscientiousness and agreeableness by 1 SD in any direction, but they wouldn’t be able to change any other personality trait. I hypothesize that factor C is log-normally distributed in the general population, with a mean of 2 and an SD of 1.4.
Some personality traits are probably harder to change than others, and some directions are harder to change than others. For instance, it is harder to become more conscientious than less conscientious. Some traits probably cannot be changed at all without drug or interventions, such as neuroticism. Because of this, there is also a stickiness factor s, which alters the amount of C needed to change a trait by a standard deviation. For example, if increasing extroversion has a s factor of 0.3, investing 1 C in ir would increase extroversion by 0.3 SD. My starting assumptions for the s values of the following traits/directions are the following:
Increase extroversion: 0.3
Decrease extroversion: 0.4
Increase neuroticism: 0.1 (no drugs)
Decrease neuroticism: 0.05 (no drugs)
Increase conscientiousness: 0.15
Decrease conscientiousness: 1
Increase agreeableness: 0.4
Decrease agreeableness: 0.6
Increase openness: 0.25
Decrease openness: 0.6
Increase p-factor: 0.2
Decrease p-factor: 0
I also polled my followers on this twice, and they seem to think that the s factor rank order is neuroticism < conscientiousness < agreeableness < extroversion < openness. I agree that neur/conscientiousness are the hardest to change (especially if you ignore that decreasing conscientiousness is very easy), but I think the rank order for the other three traits should be reversed.
I assume these changes in personality do not work the same for each trait - I think that increasing/decreasing agreeableness would be easy in the short term, but hard in the long term. On the other hand, I think that attempts to improve conscientiousness would be more stable in the long term. Sub-traits (e.g. assertiveness, machivellianism) are perhaps easier to change than more global traits (e.g. plasticity, agreeableness).
C probably correlates with personality - I assume it correlates moderately with conscientiousness and openness, but not much with any other trait. Given that IQ and conscientiousness do not appear to correlate much, C probably does not correlate with IQ either.