The most important skill a writer needs is the ability to go with the flow. Though you may have sat down to outline your novel, and you know exactly what you want them to do and when, it doesn't always happen that way. As you write, you will learn your characters. They may become someone you never expected them to, and sometimes they refuse to do what you want them to do.
Often it is when you try to make the character fit the mold created in your mind that you get writers block. I've found that the only way to overcome this is to sit down, write, and let your characters do the talking.
When I sat down to write my novel No Matter What I had two main characters in mind with several secondary characters. Though I never intended for Blake (one of those secondary characters) to play a role that was vital, the novel would not be the same if he had not. I found that as I wrote, Blake wanted to do his own thing, and as an author, I spent many an hour trying to make him do something differently. In the end, Blake won the battle and I let him be who he wanted to be.
That's not to say that you should not write an outline. Outlines are very useful tools for completing your project. There are many different ways of outlining a project. My personal style is to outline as I write. What I mean is that I write a chapter then go back and review it. Once I have reviewed that chapter, I outline what I want to happen in the next chapter. Some people write and outline at the beginning. There are pro's for writing and outline and there are pro's for not writing an outline. Ultimately, it is up to you--the author--to decide if you work better with or without one.
Remember that it is your story, but it is vital to have realistic characters. Forcing a character to go in a direction that is not true to the character makes that character less believable and will jeopardize the quality of your writing. That doesn't mean that you have no say so, but it does mean that when you are stuck, try just letting it flow, you might find an interesting twist that you didn't think of but your character did.