The librarian

In the morning, Ren Xiaosu was doing some reading in the library. Meanwhile, An Yuqian was snoring loudly as he slept in his chair at the entrance.

When the sun shone onto An Yuqian's face from the outside, he would even cover his face with a book to shield himself from the light.

Every morning, when Ren Xiaosu arrived, he would automatically give ten yuan to An Yuqian. Moreover, there was no need for Ren Xiaosu to keep calling An Yuqian anymore as he would be waiting at the door every day at 8.30 AM sharp while yawning.

Gradually, An Yuqian found it extremely uncomfortable that he had to always sleep like that. He used to always play mahjong throughout the night before heading home to sleep well during the morning. But since Ren Xiaosu started coming to the library, he could only sleep while sitting in his chair at the library.

How could sleeping in a chair be more comfortable than sleeping in a bed?