Substitution is quickly taking on a new activity or relationship to avoid experiencing frustration or disappointment in a present relationship or activity. Rebound relationships are recognized to work this way. Present disappointment or rejection reminds a person of early failures and so gives rise to shame. However, working through a stalemate or obstacle is what provides new experiences and provides ego strength and flexibility
It is common advice to start something new to get over something, and the ending of something can be an opportunity. We have an economic life now based on novelty, and it is expected that everyone will want to ''go after' the 'latest thing.' Hidden in this constant churning often is a shrinking away from an emotional challenge of some sort.
Usually the substitution involves dropping the previous interest rather than resolving the problem, enriching the relationship, or working through the shame feelings. Idealistic or fantasized 'success' is valued more than the depth of relationship, and so serial substitution is encouraged until some easy success is found, but such successes do not provide satisfaction.
Psychotherapy undertaken when a relationship has ended or is ending may flounder because unconsciously it is being used as a substitute, and the engagement is therefore superficial.