Why did Mandela say that it was almost impossible for a man of his race to fulfil both of those obligations in a country like South Africa?
Mandela said so because the system of racial segregation was practiced in South Africa. In those times, blacks who attempted to live as a human beings were severely punished and isolated. Those who tried to fulfil their duty towards people were inevitably ripped off from their families. They were forced to live a life apart, rebelling in secrecy.