I am not sure, if you can say, that the selection process is hard work.
If you have the required ability, you will succeed.
If you don t succeed, especially to take the last hurdle, where is checked, if you fullfill the airlines specific profile... this has something to mean .. in my opinion at least.
I do know some guys, that failed to take this and not just with one airline... went to flight school, spend a load of money to get ther licence.. and then, when it s about finding a job, they face same hurdle again... unfortunately they never made it to a major airline.
So, the risk is very high, to end with debts and no work...