In other words, yes, people with clinical depression find that it gets in the way of their daily life. His hypothesis is about why normal, healthy people suffer from low mood / mild depression from time-to-time, and what evolutionary advantage that might give us.
It certainly plays out that way in actual medical cases, and cognitive therapy for depression is all about showing patients that they can still succeed in goal-directed behavior.
If depressed people despair that they cannot find new friends or lose some weight, maybe the depression might direct them to try something new. That's how I see the idea presented here. (Unfortunately, you're right that many people are quick to give up and deem a goal impossible.)