I know in the past sometimes I erased something from a .htaccess file without considering what was in the .htaccess files "upstream" per-se.
For example, if I had a redirect in the .htaccess file for the URL
http://www.myDomain.com/awesomeProduct to point to
http://www.myDomain.com/awesomeProduct/manual and deleted that entry to no avail, perhaps there might be something in the .htaccess one directory up to do the exact same thing. In that case, that entry would also need to be removed in that .htaccess file.
Of course, the thing that always fustrated me was when I was editing a local copy of .htaccess meaning to FTP upload it, forgetting to upload the file then wondering why my server was being all "weird." Oops
