Final answer:
Reynie was worried about Sticky's late-night activities as they suggest that Sticky might be dealing with a personal issue, entangled in a dangerous situation, or jeopardizing the safety of himself or others.
Step-by-step explanation:
Reynie was worried about Sticky after he said he had been out half the night because Sticky’s behavior was indicative of something worrying or troubling happening. When characters in literature display unusual behaviors, such as staying out unexpectedly late, it often signals that they are either in some sort of distress, facing a dilemma, or involved in secretive activities.
In this context, Sticky's actions are concerning to Reynie, as they could imply that Sticky is struggling with a personal issue, entangled in a dangerous situation, or potentially jeopardizing their safety or the safety of others. The novel does not provide a definitive reason for Sticky's late-night activities, leaving the reader to infer the potential risks and causes for concern.