Once you wrap your head around it, it does make sense.
The first part is easy. If, whatever follows "because", is the reason for what's stated in the first part of the sentence, then you need a comma.
When because follows a negated verb phrase, it must be preceded by a comma when the because clause explains why the event did not occur. They didn’t want her on the committee, because she was so outspoken means roughly “Her outspokenness was their reason for not wanting her on the committee.”
This is a little tougher to understand.
When there is no comma, the because clause is included in what is being negated. Thus They didn’t want her on the committee because she was so outspoken implies that they may in fact have wanted her on the committee but for some reason other than her outspokenness.
Zdanie bez przecinka będzie inaczej zaintonowane i nie będzie pauzy przed because.
They didn't want her on the committee because she was so outspoken. (They wanted her because she had innovative ideas.)
But, I could be wrong :)