No matter how much you outline, or plan, what you’re going to write about, writing is always a leap of faith into the unknown.
When you open your mind and heart, and put pen to paper (or fingers to keyboard) you don’t know what words or ideas are going to come, or even if any are going to come at all. This can be scary or exciting, depending on how much self-confidence, trust, and experience you have.
The more you can embrace this unknowable nature of writing, the easier it will be to write. Planning is good, and even necessary at times. But it doesn’t change that writing is essentially a journey of discovery.