This is the nano peptalk I was writing for no pro this week. I have a headache so I have to revise it later to be more chatty, I just had to get it written.
Characters are Complicated
A lot of non-writers think we're nuts when we say a character did something we weren't expecting, but it's because we have given them a life of their own and they act and react accordingly. Of course, this means they can decide they want to take up pea stacking and we are powerless to stop them. If you haven't had a character go rogue on you yet, you will.
Before you panic, remember that to have an unruly character, you first must have a well-developed character with a distinct personality and voice. That means you have achieved a form of greatness many aspire to. If you're not there yet, the more you write as that character, the more intuitive they'll become, it just takes time. Either you're putting in the effort needed to make them come alive, or they already have come alive, and both mean you rock.