In the 1950s and 1960s there were far more aircraft accidents as a proportion of the world transport fleets. Many then seemed to have a number of causes or contributing factors, often three or more. Many of these contributing factors have been "designed out". Systems have become more reliable, enabling very high and profitable utilisations.
" Simple things", like Checklists and Weather Minima, better landing aids, Flight Time limitations, Aquaplaning, Aircraft Performance calculation graphs were some of the items which only ultimately were to reach my level of knowledge as a First Officer. Some of this may have been known elsewhere in a Company, but prior to photocopying, much would have been kept in a Head Office drawer !
Flying training required, then, for a F/O was 6 T/Os and Landings, by day.
A Captain only had to do 5, some at night and with an engine failure.
( With this level of training......... !)
(If I exceeded 125 hours flying in a month, I would require a further medical ("to see if I was fit for a further 125 hours," it was said. !))