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He had been pulling out bad flashing when the wasp had gotten him.

The ironic part was that he warned himself each time he climbed onto the roof to keep an eye out for nests; he had gotten that bug bomb just in case. But this morning the stillness and peace had been so complete that his watchfulness had lapsed. He had been back in the world of the play he was slowly creating, roughing out whatever scene he would be working on that evening in his head. The play was going very well, and although Wendy had said little, he knew she was pleased. He had been roadblocked on the crucial scene between Denker, the sadistic headmaster, and Gary Benson, his young hero, during the last unhappy six months at Stovington, months when the craving for a drink had been so bad that he could barely concentrate on his in-class lectures, let alone his extracurricular literary ambitions.Question: What’s the relationship BETWEEN ‘But this morning the stillness and peace had been so complete that his watchfulness had lapsed’ AND ‘He had been back in the world of the play he was slowly creating, roughing out whatever scene he would be working on that evening in his head?’

Question

question
He had been pulling out bad flashing when the wasp had gotten him.

The ironic part was that he warned himself each time he climbed onto the roof to keep an eye out for nests; he had gotten that bug bomb just in case. But this morning the stillness and peace had been so complete that his watchfulness had lapsed. He had been back in the world of the play he was slowly creating, roughing out whatever scene he would be working on that evening in his head. The play was going very well, and although Wendy had said little, he knew she was pleased. He had been roadblocked on the crucial scene between Denker, the sadistic headmaster, and Gary Benson, his young hero, during the last unhappy six months at Stovington, months when the craving for a drink had been so bad that he could barely concentrate on his in-class lectures, let alone his extracurricular literary ambitions.Question: What’s the relationship BETWEEN ‘But this morning the stillness and peace had been so complete that his watchfulness had lapsed’ AND ‘He had been back in the world of the play he was slowly creating, roughing out whatever scene he would be working on that evening in his head?’

Answer

It think the author is trying to explain why the character wasn't concentrating as much as he should have been. It was a particularly calm morning and since there was no distraction, he let his thoughts wander off, thinking about his play. He wasn't paying attention because he was "in his own world". If he'd heard buzzing or other noise, he would have been more alert.

Answer

Question: What’s the relationship BETWEEN ‘But this morning the stillness and peace had been so complete that his watchfulness had lapsed’ AND ‘He had been back in the world of the play he was slowly creating, roughing out whatever scene he would be working on that evening in his head?’

I would say that the link is this - because it was so quiet, e.g no sound of wasps buzzing (or anything else), he allowed his mind to drift to other things. If there had been a lot of noise in the background he might have been more alert, more in the present moment, focused on what he was doing. Because it was quiet however his mind drifted to what was more important to him, the play etc.