Final answer:
The psychologist who believed in a pessimistic explanatory style is Martin Seligman. His research on learned helplessness and depression emphasized the role of internal, global, and stable attributions in the development of depressive symptoms, but also pointed out that attribution styles can be changed.
Step-by-step explanation:
The psychologist who believed that some people tend to have a pessimistic explanatory style, characterized by the tendency to blame bad events on themselves, is Martin Seligman. Seligman's research, alongside his colleagues, led to the reformulation of the learned helplessness model and introduced the concept of attributions that contribute to depression. In this context, attributions refer to how individuals explain the causes of events and behaviors. If a person consistently makes internal, global, and stable attributions for negative events, they are more likely to develop depression. Seligman emphasized that this explanatory style could lead to a sense of learned helplessness and eventually to depression. However, it was also found that attribution styles could be changed with practice, potentially reducing the vulnerability to depression.