When you don't have time to think about where your notes should go, just click Window logo key + N which immediately launches ...

When you don't have time to think about where your notes should go, just click Window logo key + N which immediately launches OneNote and creates a new page in the Unfiled Notes section (click the button at the bottom of the Navigation Bar to jump to it later). It's okay if this section gets big. You can drag the pages to other sections later, or just use search to find them in this section.