You'll have to forgive my attempts at examplifying this to get the point across without breaking TOS.
I have a website:
www.nobluewidgets.co.uk
it's the name of the site and most people link to it using "no blue widgets" as the linking text. But:
for "blue widgets" I rank No.1
for "no blue widets" I rank No.3
The No. 1 ranking for "no blue widgets" is an inner page of a site talking about our "no blue widgets" site - that page has no external backlinks to it. The No. 2 ranking for "no blue widgets" isn't even in the top 30 for "blue widgets".
Is this an example of Over-Optimisation filtration? Is being "no blue widgets" in every sense stopping us from ranking for "no blue widgets"?