Some five years ago, I wrote on "Gaining a Pilot's Brevet in WWII":
..."
The first ten hours of military flying instruction are critical. This is where the sheep are sorted from the goats. In civil life, a flying club will keep on taking your money till the cows come home, irrespective of whether you're ever going to make a pilot. The [US] Army can't afford to do this, it's working to a timetable.
An average pupil will go solo after eight hours. Nine hours is stretching it. Ten, and your instructor will hand you over to a check pilot, who will take you up and assess your performance, and who may give you a second chance, with a different instructor. But this rarely happens. You're "washed out".
It sounds hard-hearted, and we think of late developers and helping lame dogs over stiles. But, as is pointed out, your dog is still lame after you've got him over the stile, and there are more stiles ahead. Better to chop him now.
The majority of these losses took place in the first ten days. After that they became progressively fewer. One of my room mates disappeared after a month, having absent-mindedly blundered through the circuit at our Relief Landing Ground. "Dangerous tendencies", they said, and he was out. Two others had fallen at the first hurdle, so now I had the room to myself.
The Arnold Scheme had a "washout" rate of around 50%, I believe. Whether this was due to the impossibly high standards [of the US Army Air Corps], or whether simple arithmetic had more to do with it, I have often wondered..."
Time is the currency of War !