Org is implemented on top of Outline mode. Outlines allow a document
to be organized in a hierarchical structure, which, least for me, is
the best representation of notes and thoughts. An overview of this
structure is achieved by folding, i.e., hiding large parts of the
document to show only the general document structure and the parts
currently being worked on. Org greatly simplifies the use of outlines
by compressing the entire show and hide functionalities into a single
org-cycle, which is bound to the TAB key.