What People Believe
One of the most common relationship dilemmas is the tension between accepting a partner as they are and hoping — or trying — to change them. Some people enter relationships believing that love will naturally transform a partner's problematic behaviours. Others believe that people are fundamentally fixed and that trying to change someone is futile and disrespectful. Both positions are, in different ways, wrong.
What the Research Actually Shows
The most robust finding in personality development research is that people do change — substantially — over the course of their lives. A landmark 2006 meta-analysis by Roberts, Walton, and Viechtbauer, covering 92 longitudinal studies, found that personality traits shift meaningfully across adulthood, with Conscientiousness and Agreeableness tending to increase and Neuroticism tending to decrease. The idea that personality is fixed after a certain age is not supported by the evidence.
However, the mechanism of change matters enormously. Self-Determination Theory (Deci & Ryan, 2000) — one of the most empirically supported theories of human motivation — distinguishes between intrinsic motivation (change driven by personal values and genuine desire) and extrinsic motivation (change driven by external pressure, reward, or avoidance of punishment). Intrinsically motivated change is durable. Extrinsically motivated change is fragile and often produces reactance — the opposite of the desired behaviour.
For relationships specifically, a 2013 study by Finkel and colleagues found that partner pressure had a small and unreliable effect on lasting behaviour change. More strikingly, a 2014 study by Marigold, Holmes, and Ross found that people were four times more likely to make genuine behavioural changes when their partner expressed acceptance and appreciation rather than criticism and demands.
"People are four times more likely to make genuine behavioural changes when their partner expresses acceptance rather than criticism."— Marigold, D.C., Holmes, J.G. & Ross, M. (2014). Fostering relationship resilience. Journal of Personality and Social Psychology.
The Paradox of Acceptance
One of the most counterintuitive findings in relationship psychology is what Carl Rogers called the 'paradox of change': genuine change is most likely to occur when a person feels fully accepted as they are. This is not a passive resignation to the status quo — it is the recognition that safety and acceptance create the psychological conditions in which growth becomes possible.
When a partner feels criticised, pressured, or conditionally accepted, they become defensive. Defensiveness is one of Gottman's — a reliable predictor of relationship deterioration. The partner's energy goes into self-protection rather than growth. Conversely, when a partner feels genuinely accepted, they are more open to feedback, more willing to examine their own behaviour, and more motivated to change for their own reasons.
What This Means for Your Relationships
The practical implication is clear: if you want your partner to change, the most effective strategy is not to pressure them but to create the conditions in which change becomes attractive to them. This means expressing appreciation for who they already are, making specific requests rather than global criticisms, and modelling the behaviour you want to see.
It also means being honest with yourself about what you are actually asking. There is a meaningful difference between asking a partner to change a specific behaviour (arriving on time, reducing drinking, communicating more openly) and asking them to change a fundamental aspect of their character. The former is reasonable and achievable. The latter is asking someone to become a different person — and that is not something you can or should try to engineer.
People can and do change, but only when intrinsically motivated. Partner pressure reliably backfires. The most effective strategy for encouraging change is expressing genuine acceptance — the paradox of change is that it requires letting go of the demand for it.