Final answer:
Paul finds his leave unbearable due to idleness, costly living without work, unfavorable environmental conditions, and intense mental discomfort. He reflects on returning to his previous job to escape these feelings of agony and frustration.
Step-by-step explanation:
When Paul is on leave, he finds the situation unbearable due to several factors. Firstly, he feels the burden of being idle when he mentions, 'It's too expensive to stay here doing nothing', emphasizing his need for productive work.
Additionally, the physical environment is distressing to him as indicated by, 'the fields are full of water', which probably means that bad weather conditions are contributing to his discomfort.
Moreover, there is a suggestion of emotional turmoil where he says, 'the agony. I can't stand it...', which seems to stem from his frustration over his current circumstances. His resolve to go back from where he came from is an indication of his inability to contend with the present discomforts.
The anxiety and pressures are also reflected in a different narrative, where one character struggles with feelings of inadequacy and nervousness represented by the text: 'These nervous troubles are dreadfully depressing'. This reveals an inner conflict and the weight of expectations against personal limitations.