"When Stark isn't off sulking somewhere, or whatever he's doing when he won't return my calls, I alternate between the two. That usually works well, though occasionally an idea for the wrong guy drifts through my mind"

This quote is likely referring to 2 different people, Stark and another person. It appears that Stark is somebody who is typically not readily available, either due to the fact that he is sulking or not returning calls. The speaker is likely referring to two various individuals when they say they alternate between the two. This suggests that the speaker has two different people they rely on when they require help or suggestions. Nevertheless, in some cases the speaker gets puzzled and has an idea for the wrong individual. This might be because the 2 individuals are comparable in some way, or because the speaker is so utilized to rotating between the two that they in some cases forget who they are thinking about. This quote is a tip that it is essential to be mindful of who you are thinking of when you have a concept or require assistance.