The speaker begins with a quiet admission: they haven't achieved as much as they would like. It's a familiar feeling of falling short of your own hopes. Instead of dwelling on it, they say they respond by keeping all doubt "locked up." The title, "Jailer," casts the speaker as a guard whose job is to hold doubt in a cell so it can't interfere.
The last two lines complicate that confidence. The speaker calls doubt "a nonsensical thing," as if it deserves no attention, yet admits to fearing it as "a cousin of the hive." The hive suggests a swarm of buzzing, restless thoughts that could multiply and sting. Doubt may be locked away, but the speaker still sounds wary of it.
The mood is tense and guarded. The tone is calm on the surface, but the need for a jailer hints that the doubt is not easily controlled. The poem suggests that suppressing self-doubt may be a way of managing it, not a way of getting rid of it.