I UNDERSTAND! I UNDERSTAND MS. MATILDA'S WRITER PROBLEMS VERY WELL!!
You've thought everything out, typed the outline, started making the chapters, and to only have the story go to whole new direction and just ahdsjkkjahd GIVE ME BACK THE DAYS I SPENT THINKING ABOUT YOU!!
Sometimes, it's good, and sometimes, it's not. Especially if there'll be holes in the story, you'd have to brainstorm how to refill that if you're going to the other direction, and it can be stressful if it's a complex story :T