A person feels as comfortable as possible when he feels control over himself and his environment. Poor software deprives users of control: unexpected interactions, confusing processes and unpredictable results are imposed on people. Give users a sense of control: keep them regularly informed about the state of the system, show causal relationships (if you do this, it will be) and tell them what to expect at each stage. Don’t be afraid to repeat the obvious … evidence is generally a relative concept.