Socio-Cognitive Model of Trust: Quantitative Aspects - Trust Theory: A Socio-Cognitive and Computational Model - page 106

In other words, either Ag 1 's trust of Ag 2 is the same but her preferences have changed
(including her attitude towards risk), or Ag 1 has changed her evaluations and predictions about
relying on Ag 2 . Another important role is played by the control (see Chapter 7) that can allow
delegation also to be given to a not very trusted agent. For an analysis on this relationship see
(Castelfranchi and Falcone, 2000)).
3.7 When Trust Is Too Few or Too Much
Trust is not always rational or adaptive and profitable. Let's see when it is rational or irrational,
and when it is not useful, although well grounded.
3.7.1 Rational Trust
In our view trust can be rational and can support rational decisions. Trust as attitude ( core Trust )
is epistemically rational when it is reason-based. When it is based on well motivated evidence
and on good inferences, when its constitutive beliefs are well grounded (their credibility is
correctly based on external and internal credible sources); when the evaluation is realistic and
the esteem is justified, not mere faith.
The decision/action of trusting is rational when it is based on an epistemically rational
attitude and on a sufficient degree relative to the perceived risk. If my expectation is well
grounded and the degree of trust exceeds the perceived risk, my decision to trust is subjectively
rational. 15
To trust is indeed irrational either when the accepted risk is too high (relative to the degree
of trust), or when trust is not based on good evidence, is not well supported. Either the faith
component (unwarranted expectations) or the risk acceptance (blind trust) are too high. 16
3.7.2 Over-Confidence and Over-Diffidence
Trust is not always good - also in cooperation and organization. It can be dangerous both for
the individual and for the organization. In fact the consequences of over-confidence (the excess
of trust) at the individual level are: reduced control actions; additional risks; non careful and
non accurate action; distraction; delay in repair; possible partial or total failure, or additional
cost for recovering.
The same is true in collective activity. But, what does 'over-confidence' i.e. excess of trust
actually mean? In our model it means that X accepts too much risk or too much ignorance,
or is not accurate in her evaluations. Noticed that there cannot be too much positive trust, or
esteem of Y . It can be not well grounded and then badly placed: the actual risk is greater than
the subjective one. Positive evaluation on Y (trust in Y ) can be too much only in the sense
that it is more than that reasonably needed for delegating to Y . In this case, X is too prudent
and has searched for too much evidence and information. Since also knowledge has costs and
15 For a more detailed discussion about rational and irrational motive for trust see Chapter 8, Section 8.1.
16 Rational trust can be based not only on reasons and reasoning, on explicit evaluations and beliefs, but also
on simple learning and experience. For example the prediction of the event or result can be based not on some
understanding of the process or some model of it, but just on repeated experiences and associations.