Recruitment. Just like any other sales job, recruitment has its ups and downs. But the critical difference is that in recruitment your main work is with people. And people can be unpredictable.
Sometimes candidates can take recruiters for granted. They might go through the whole process of trying for a job but are not really interested in switching careers. To a candidate, it seems harmless. You read a job description, do some interviews, and then go back to your original job. Sometimes candidates do that to know more about the market. Sometimes they do it to get a raise at their current workplace. Or sometimes they are just bored. But for the recruiter, it isn’t harmless. It has the opposite effect.
Humans are unpredictable. So are the candidates. This unpredictable nature makes the job very difficult. People are never 100% sure about their decisions. The recruiter can try and help the candidate. But ultimately it’s up to the candidate. This nature of the job makes the job very difficult for a lot of people.