Hoa Lorander describes in her article about the Negativity Bias in User Experience how bad experiences will stay in the head of people. She describes how difficult it is to overcome this experience with good ones.
Summary: People remember the bad more than the good. Users’ tendency to identify flaws in designs raises the bar for what they consider acceptable.
A really well framed advice at the end of the article.
Test, test, and then test: Focus on designing usable websites that solve users’ problems. Understand your users and their tasks, and go out of your way to iron out as many usability hurdles (negative encounters) as you can in order to make it easy for people to reach their goals.