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Self-Expansion Model: How Relationships Grow (and Stagnate) Us

Evidence-based practices for sustaining closeness and personal growth through the self-expansion mechanism

Why relationships feel exciting at first, and how to keep it

Self-expansion is Arthur and Elaine Aron’s account of a basic human motivation: people are driven to grow — to expand their sense of self by incorporating new perspectives, skills, and resources — and relationships are so motivating early on because they represent the fastest available route to that expansion. A new partner supplies perspectives, capabilities, and social worlds you did not have, and the rate of expansion is experienced as excitement. That explains the part people find puzzling: closeness often fades not because affection decreased but because the rate of expansion did — you have already absorbed most of what the other person brought. The well-studied practical implication follows directly: doing novel, moderately challenging activities together restarts expansion and revitalises closeness. The model has a substantial empirical base, primarily in romantic relationships.

Arthur Aron and colleagues proposed that humans have a fundamental motivation to expand the self — to grow more capable, knowledgeable, and connected. Relationships are initially exhilarating because they are the fastest route to self-expansion: a new person brings perspectives, experiences, and capabilities you did not have. When the novelty ends, expansion stalls — and the relationship can feel stagnant not because affection decreased but because growth stopped. That distinction is the reason the model is useful rather than merely descriptive: if the felt problem were lost affection there would be little to do about it, but if the felt problem is a stalled expansion rate, it is addressable — you can deliberately reintroduce the novelty and challenge that produced expansion in the first place. This is relationship science rather than self-help: the model was developed and tested by Arthur and Elaine Aron across several decades of published studies. The practices below are grounded in that research programme, with honest notes on what the evidence directly supports.

Practices

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Research

  • Aron, Norman, Aron, McKenna & Heyman (2000), "Couples’s shared participation in novel and arousing activities and experienced relationship quality", Journal of Personality and Social Psychology
  • Aron, Aron & Smollan (1992), "Inclusion of Other in the Self Scale and the structure of interpersonal closeness", Journal of Personality and Social Psychology
  • Feeney & Collins (2015), "A new look at social support: A theoretical perspective on thriving through relationships", Personality and Social Psychology Review
  • Aron, Melinat, Aron, Vallone & Bator (1997), "The experimental generation of interpersonal closeness", Personality and Social Psychology Bulletin
  • Aron et al. (2000), shared novel activities and relationship quality, JPSP

Related concepts

Frequently asked questions

Why relationships feel exciting at first, and how to keep it

Self-expansion is Arthur and Elaine Aron’s account of a basic human motivation: people are driven to grow — to expand their sense of self by incorporating new perspectives, skills, and resources — and relationships are so motivating early on because they represent the fastest available route to that expansion. A new partner supplies perspectives, capabilities, and social worlds you did not have, and the rate of expansion is experienced as excitement. That explains the part people find puzzling: closeness often fades not because affection decreased but because the rate of expansion did — you have already absorbed most of what the other person brought. The well-studied practical implication follows directly: doing novel, moderately challenging activities together restarts expansion and revitalises closeness. The model has a substantial empirical base, primarily in romantic relationships.

How do you do novel, moderately challenging activities together?

When two people do something novel and moderately challenging together, they both expand — acquiring new capabilities and perspectives. The brain associates this expansion experience with the partner who was present, restoring the early-relationship "glow" that came from rapid natural expansion. The key variables are novelty and mild challenge: familiar, easy activities do not produce the same effect even if enjoyable.

How do you practise including the other person in your self-concept?

Aron’s model holds that closeness is operationally defined as the degree to which a person incorporates the other into their self-concept — borrows their perspectives, skills, and identity. This is not metaphor: research using reaction-time paradigms shows people are slower to distinguish self from close-other attributes the closer the relationship. Practices that deliberately invoke the other’s perspective strengthen this inclusion and deepen the experience of closeness.

Pursue personal growth that you share: how do you not parallel but joint?

Individual growth pursued privately does not activate the self-expansion-via-other mechanism. When growth is shared — each person expands, and the expansion is visible and reciprocally incorporated — the relationship itself becomes a vehicle for the most fundamental human motivation the model identifies. The vehicle effect makes the relationship feel alive and central rather than a comfortable backdrop to individual achievement.

How do you audit current relationships for expansion rate?

If self-expansion is a motivation, its absence will be experienced as malaise or a diffuse sense of stagnation without an obvious cause. Periodic audit — asking "what new perspective, capability, or experience has this relationship brought me in the past three months?" — surfaces expansion rate as a trackable variable. Low rate is not evidence of failure but a signal to redesign how the relationship is spent.

How do you use structured escalating self-disclosure to accelerate closeness?

Aron’s "36 questions" research demonstrated that sustained, reciprocal self-disclosure — starting with easy topics and gradually deepening — reliably generates closeness in pairs of strangers. The mechanism is mutual vulnerability and reciprocal self-expansion: each disclosure offers the other person new material to incorporate into their self-concept, and the progressiveness ensures comfort at each depth level before descending further.

How do you protect expansion by resisting the slide into pure comfort?

Habituation reduces the subjective salience of familiar stimuli; in relationships, this means the expansion that once happened naturally — because everything was new — must now be deliberately engineered because the partner is deeply known. The motivation does not disappear; the natural supply of novelty does. Relationships that remain satisfying long-term are those where the partners actively introduce new shared experiences rather than relying on the natural flow of events.

How do you apply the self-expansion framework to individual growth, not only relationships?

The self-expansion model does not require a partner; it proposes a general human motivation to expand. Individual pursuit of genuinely new skills, domains, or perspectives activates the same expansion mechanism. The motivational quality of "flow" and "meaning" in solo contexts is consistent with expansion: engaged novelty and challenge produce the felt sense of growing that the model identifies as intrinsically rewarding.