The visual editor provides a visual editor to write and format posts. However, it tries to format the HTML tags written in the HTML editor when turning to the visual editor, and may delete some HTML tags and screw up HTML tags. Even when we set the editor to HTML editor, WordPress may automatically turn back to visual editor next time when we edit a post. For users that are familiar with HTML editor and prefer it, it is better to disable the Visual Editor completely. The WordPress provides an option for us to disable the visual editor actually.
We can log in WordPress, go to Users->Your Profile, and check the box for "Disable visual editor when writing" to disabled it. The the visual editor will be turned off.
Additionally, the administrators of WordPress you can edit each user’s option and disable the visual editor from the Users->All Users panel.