There are two parts to this. There certainly are some individuals who are required to leave the military because they are not a good fit for the military. This usually happens in the first year to three years of military service. On occasion it's because they're unable to meet the training requirements or meet the performance requirements. On some occasions, it's because of their professional conduct. There were certainly instances in the news recently of cases of young people joining who were not displaying professional conduct out on the west coast. The military can engage in remedial action, trying to assist these people to understand the values, the standards and the behaviours, but on occasion, they're not a good fit and they leave.
The other reason, of course, is that, as I said, a large number of Canadians have limited knowledge of the military. As much as the recruiting system tries to inform them, once they join and find out what military life is really like, for example what army camping really consists of or that going to sea on the North Atlantic is not like canoeing on Lake Ontario, there are people who realize it's not a good fit for them.
In the long term, for those who get past that initial adjustment, the real reasons for people leaving have to do with work-life balance and all the pressures on families.