The phrase "there's a thin/fine line between" is used to describe two things that are very similar, despite having some key differences. It highlights a subtle distinction between two concepts, ideas, or actions where one can easily transition into the other, but one is acceptable and the other is not.
- From online with editing
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What prompted me to APAD 
this phrase is the story of math genius and Nodel laureate John Nash.
You probably also watched the movie "A beautiful mind" based on his biography with the same name. I was so touched by the movie, I bought the book and kept it with me till today (see pic below).
"There is a thin line between genius and madness". But in Nash's case, that line is so blurred that the two became the same thing!!! 
The phrase can be used many other ways: eg. there is a thin line between fear and caution, between love and hate, between too much and not enough, ..., etc.
But one may never have enough fresh cherry tomatoes 
Cheers to all!
Note the cherry tomatoes were picked yesterday from our very own garden plots!
