Why are guys getting thru on 3rd/4th attempt? If they are good enough the 3rd time then surely they are good enough the first time
Depends on the individual guy/gal and I would imagine it is impossible to generalise. Possible reasons I can think of for a first time failure passing on further attempts are:
Generally competent but too young/immature - improves with age/experience.
Poor performance on tests - possibly underprepared for things such as the maths - if you haven't had to do basic maths for over 15 years working out things such as the areas of squares based on dividing into triangles with the only dimensions given as the diameter of a circle in 20 seconds or so can trip you up! The info given prior to selection day was quite misleading!
A personality clash with the interviewer (some people have more 'clashes' than others but you could just be unlucky)
A poor 'I know it all' attitude which is diluted eventually as you realise after a few years that the big carriers won't give you a job and you become slightly more humble.
'Breezing' tests such as the group tests. I am sure that the RAF/Army/Navy officer who walks into the group test, takes charge, delegates then comes up with a solution in 10 mins thinks they have done a great job. In an officer selection test they would have but I don't see tham getting a sim ride in civil aviation following it.
There must be many more but those are just off the top of my head..... But to reiterate the main point - in order to know why a first time failure can pass later you have to know all the reasons behind that failure.