Watch: James Haskell backs Prince Harry book: 'You can't let people keep walking over you'
Former rugby player Haskell, 37, joined his father-in-law Richard Madeley on Wednesday's Good Morning Britain to talk about his own new wellbeing book, and gave his views on Harry's autobiography which was published this week.
He told Madeley and Susanna Reid that he thought it was an important way of Harry being able to share his truth about events from his life and stick up for himself.
Haskell, who is married to Chloe Madeley, said: "So many people in his position never get to comment and so much of what he says is either down to what a journalist has interpreted or what a soundbite has been edited."
Reid asked whether Haskell thought Harry needed to accept he could not control what was interpreted from his comments.
He said: "On the whole, you're right, but actually in particular cases we would never have got anywhere in life if people kept laying down and letting other people walk over them.
"If Emily Pankhurst had never done what she done, women wouldn't have achieved what they've achieved, if Rosa Parks hadn't said I'm not going to get up, certain things wouldn't have happened.
"I'm not likening Harry to them, but I'm saying in respect of standing up for something, you can't let people keep walking over you."
Haskell continued: "For someone like him, there are so many conflicting narratives, I think you've got to put a tentpole in the ground, you've got to turn around and say listen, all the furore, here is my truth. This is undeniably what I believe.
"Even his mother, the interview towards the end of her life, so many people questioned what she'd said...when Diana was alive, everyone wanted to have a go, as soon as she sadly passed away, everyone was best of friends.
"He's put it out there, now he can move on because it's undeniable what he's said. People can make interpretations, he can say, 'no, no - look back at the book. That's what happened, that's what I believe.'"
But Madeley told his son-in-law that Harry could benefit from his advice on taking accountability.
Madeley said: "You talk about not blaming the world for your problems, but looking into your own back garden. That's a conversation you could have with Harry, because he doesn't accept any responsibility for anything that's gone wrong with his life.
"Everything's everyone else's fault."
Haskell replied: "I think it's very important with that to get your own view and own narrative across. He can only tell his story."