Final answer:
Pi, presumably a fictional character, has chosen to stop writing due to reasons that might be inferred by the reader but are not explicitly stated in the provided text.
Step-by-step explanation:
The character Pi is unable to write in the diary because he is a fictional character in the narrative who has decided to stop writing. This scenario is likely from a story or novel where the character named Pi or Bartleby expresses a loss of will or disinterest in the act of writing, despite being asked to continue. Without further context, it's not clear if the inactivity is due to a physical inability, a lack of motivation, or an existential choice.