Matt Damon says fatigue is the hardest part of parenthood.The actor has three daughters - Isabella, six, Gia Zalava, four and Stella Zavala, two - with his wife Luciana Barroso and admitted lack of sleep is like waiting for the Navy SEALS to attack.He told Independent Radar magazine: "[Fatherhood] is something I've always wanted to do. Although sleeplessness is the toughest part."Sometimes you're looking at the clock in the middle of the night and it's the time the Navy SEALS are usually sent to kill you. That's hard."And although he is a family man and widely seen as likeable, the 42-year-old star isn't sure why people actually like him so much.He admitted: "[Niceness] is not something I set out to achieve by holding myself to a certain standard of behaviour."I don't know why people like me. I'm glad they do - and I'm glad they still go and see my movies."Despite this, his new film 'Promised Land' for its portrayal of fracking - the extraction of underground gas - and of farmers opposing it.He argued: "I don't think it deserves this kind of withering attack. There isn't a scene in the movie that I would change or do differently, but it didn't get the reception I hoped for."Sometimes people find movies later on, and I personally love it. I really don't understand the criticism, that I've been hearing back."