I take the example of Nelson Mandela, who lived serving his people. He never thought that he would be a symbol of justice and freedom.

How can you know? At some point he likely recognised his own influence and that will have affected his future action from that point. He was not a blind man, he aid attention so it is unlikely that he missed it.

I've read about the Beatles but never heard any of their songs.

Really?

They simple just did what they loved doing--making good music, without paying so much attention as to leaving a legacy, which they did.

This is what everyone should be doing.