blastn cut off values

Question

[Wilber0x]

I am using blast to search for genes present within plastid genomes. I am trying to work out what causes blast to find a hit

I am using blastn with completely default settings to find any matches. What are the parameters that determine when a match is found or not? I am not filtering by e-value, just using all the hits blastn returns.

[Arsenal]

Confusing question.

First of all, where are you running blast? Against which databases?

Then,

what causes blast to find a hit

What are the parameters that determine when a match is found or not

That's literally one of the most well documented information of blast manual. Please, tell me you've read it.

And

I am not filtering by e-value, just using all the hits blastn returns

W H Y ?