The line above is taken from the poem “The Pencil’s Story’. It is written by Florence Hoatson, an English poet. In this poem, she pictures the life of a pencil. A pencil is useful to everyone in a household. From a small boy to the housemaker everyone uses the pencil for writing various things. Therefore, it leads a very busy life. In the poem, the pencil narrates its daily routine.
Whenever a pencil is used, with continuous writing, it becomes blunt. So, it has to be sharpened with a knife to make it usable. So, the pencil says that whenever its wits are rather dull, meaning, whenever it becomes blunt, it is sharpened with a knife.