Can anyone share, at least for the first 2 years in Big 4, is the work tough because:
1. Long hours, a lot of work to be done but quite simple/mundane work (thus more physically demanding),

or because

2. The learning curve is very steep and the work is extremely difficult (as compared to what is learnt in uni), thus more academically challenging?

I know that it probably is due to both factors, but which is it more of?
Going out to work for my first full time job soon and I'm pretty scared and wish to know what to expect roughly!

Thank you