Humans can mistakenly think that specific conditions are more likely than a general one. Formally dubbed the “conjunction fallacy”, it is also known as the Linda problem, after the oft-cited example of this cognitive failing in action:

Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, Linda was deeply concerned with issues of discrimination and social justice. She also participated in anti-nuclear demonstrations.

Which is more probable?

Linda is a bank teller.
Linda is a bank teller and is active in the feminist movement.

The majority of those asked chose option 2. After a moment of thought, it is obvious why this is ridiculous. The first option includes the possibility of the second and many other possibilities with their own likelihood.