Therapy is the only interaction I can think of (in American society, anyway) during which two people sit together for an extended period of time and the entire conversation is focused on one person. I often get the question, "don't you get bored having to listen for so long? Doesn't your mind wander?" These are two separate questions with two different answers.
I cannot think of a single time when I have been bored in my role as a therapist. There is so much to pay attention to in a therapy session that we do not pay attention to in daily conversations. At minimum, I have to pay attention to what was said, what my plan is with the client, and a multitude of factors that help me assess a client's state of mind including things like speech, motor activity, and mood. Because so much more is going on than would occur in a regular conversation with a friend, it is hard to get bored and still be a minimally competent therapist.
The other question, "does your mind ever wander," requires a more complicated answer. The short answer is, "yes." The reason for my mind wandering has never been boredom, however. Therapists are only human and I assume I speak for more than myself when I say, sometimes I have a headache, get an unexpected wave of fatigue, realize mid-session that I'm coming down with a cold, or simply didn't get good quality sleep the night before. I know I really strive to show up healthy and alert and I can usually do that because I have a small practice and I can be sure to be truly "on" during the days I'm committed to my clients. But the closer to full time a therapist is, the more of a representative sample of that person's "real life" their clients are going to get. So yes my mind does occasionally wander but it is never out of lack of interest in the client. It's almost always because minds like to wander and sometimes mine takes off before I can catch it.