Mason Currey, author of Daily Rituals: How Artists Work, writes about three procrastinating writers, Edgar Allen Poe, William James, and Franz Kafka:
In his letters, Kafka complained that his day job was holding him back, but as Louis Begley argues in his excellent biographical essay on Kafka, this was really just an excuse. Begley writes, "It is rare that writers of fiction sit behind their desks, actually writing, for more than a few hours a day. Had Kafka been able to use his time efficiently, the work schedule at the Institute would have left him with enough free time for writing. As he recognized, the truth was that he wasted time." [Highlighting mine-HR]
For the record, never refer to your reasons for not writing as "excuses," "complaints," or "whines." First, because those are negative, moralistic labels that do not add anything to the conversation: they simply shame (and, thus, undermine) you. Second, people's reasons for underproductivity are always valid. Always! 100%. I've been doing this work for more than a decade and I've never yet heard an invalid reason.
I don't know what happened to Kafka. Was he exhausted after his job, was his family life stressful, did he have trouble coping with his lack of public recognition, or was he just afraid to keep visiting the darkness that so often appeared in his writings? According to Wikipedia, "Kafka finished none of his full length novels and burned around 90 per cent of his own work," which suggests a whopping case of perfectionism.
A sad case, all around.