They say "the 1st year is the hardest"

Everyone says the first year of Marraige is the hardest. In fact I thought they were crazy since we had  dated 6 years and lived together for 1...I thought I knew him in and out...but I'm not gonna lie, it's been Hard. Some old trust issues (no cheating) Have come up, just arguing a lot. Don't get my wrong we have had some great times, but also some very tough times . Anyone else in the same boat? Is the first year of Marraige tough for a lot of people, even if we've been dating several years before?