The use of the word 'trust' in common discourse dates back to the 13th century, in Middle English. It is regarded as probably being of Scandinavian origin, akin to Old Norse traust  trust ; akin to Old English treowe  faithful . The word 'trust' dates back to much earlier though, when considered in the context of religion. Trust in God is found in both the Old and New Testaments as well as the Koran.

In current times, the religious use of trust is demonstrated in the phrase 'In God we trust', which is the official motto of the US and appears on much of its currency. Aside from the trusts found in banking and financing, 'trust' is defined in dictionaries as a 'belief that someone or something is reliable, good, effective etc.' Merriam-Webster and to 'believe that someone is good and honest and will not harm you, or that something is safe and reliable' Cambridge English .

Trust is a delicate balance. A person might ask themselves, 'Am I too trusting?' or 'Do I trust the right amount?'. These questions are probably fundamental to life itself - they are existential questions. Let me place them in the view advanced by Frank Crane, who stated: "You may be deceived if you trust too much, but you will live in torment if you do not trust enough." Is Frank correct?

There are consequences to trusting too little. Research has shown that low trust promotes psychological maladjustment. Low trust is associated with psychosocial problems such as loneliness, aggression, and low cooperation with others. Based on these findings it would be useful to develop a therapy to promote low-trust individuals' trust beliefs in others. It is important to recognise here that instilling patients' belief that the therapist is trustworthy e.g., keeps promises, keeps secrets, and is honest is the cornerstone of most forms of therapy.

For person-centred therapy in particular, the effectiveness of the therapy depends on the client holding high emotional trust beliefs which comprise the expectation that the therapist uncritically accepts personal disclosure and maintains confidentiality of it. Research has shown that priming trust cognitions by required word recall promotes trust beliefs and social engagement. If priming was integrated into Cognitive Behavioural Therapy CBT it could serve as a treatment for those individuals with low trust beliefs. Clients who have low trust beliefs in others and show concomitant psychosocial problems would be prompted during therapy to generate trusting cognitions as part of imagined social interactions. Guided by the therapist, the clients would be taught to self-prompt those trusting cognitions during real-life social interactions following the therapy sessions. The therapist would need to be mindful in this intervention of the potential consequences of trusting too much and of the objective trustworthiness of others in the clients' social relationships.

This is an edited extract from The Psychology of Trust, published by Routledge