Devils Advocate ON:
>>Really pretty common sense, but it's also been scientifically studied and proven<<
Then why are there not hundreds of crashes around the world at flight schools daily? Statistically speaking they should be falling out of the sky.
There are also those who might prefer the younger Doctor (less actual hours) who is freshly schooled in the latest techniques, procedures, etc instead of the older Doctor still doing things the way he did in 1970.