"写书是一场可怕的、令人疲惫的斗争，就像长时间的痛苦疾病一样。如果不是被某个既无法抗拒也无法理解的恶魔驱使，一个人永远不会做这样的事情。"

Simplified Meaning:

Writing a book is often a tough and tiring process. It can feel like you're going through a hard and painful time, similar to having a long-lasting sickness. Normally, nobody would choose to do something so challenging unless they felt an uncontrollable force inside them pushing them to do it. This inner force could be a deep passion, a burning need to tell a story, or a powerful desire to share a message with the world. Take, for example, a person who decides to run a marathon. Training for such a race involves hours of practice, muscle pain, and mental stress. It's not easy, and there are many moments when the person might want to quit. However, something inside them, like a dream of achieving a big goal or the joy of personal accomplishment, keeps them going despite the difficulties. In the same way, a writer is driven by a strong inner motivation to complete their book, even though the process is very demanding. This motivation can help anyone facing a hard task by reminding them of their deeper reasons and keeping them focused on their ultimate goal.