What is the hardest thing about training to become an airline pilot?

What is the hardest thing about training to become an airline pilot?

Ian Pullin (Retired British Airways Pilot) gives expert video advice on: How long does basic training take for an airline pilot?; What is the hardest thing about training to become an airline pilot?; What advice would you give to an aspiring airline pilot? and more...

The instrument flying was the hardest - the accuracy of it, and the concentrating.