Please, enlighten me - what's the score here?
This is a bit complicated. What happens in this sentence:
Przede wszystkim bądź wierny sobie, jeśli nie potrafisz włożyć w to swoje serce to odejdź.
is that the native speaker Bzibzioh replaces the genetive with an accusative in the negative sentence. I think she acts on the influence of the relatively recent phenomenon in Polish which is employing the accusative rather than the genetive with the verbs that in fact need the genetive in the affirmative statements. For example: 'ustąp mi miejsc
a' [genetive] may become 'ustąp mi miejsc
e' [accusative] in the speech of some native speakers. And although negation will change the accusative into the genetive back again even in those speakers who prefer the accusative in affirmation, Bzibzioh continues with the accusative in the negative, maybe because she is influenced by the the fact that the yet another verb which is 'potrafisz' comes before the verb 'włożyć' which makes her 'forget' about the particle 'nie'. Nevertheless, it is quite an interesting sentence which seems to have been uttered naturally and which seems to reflect the dominance of the accusative case over the genetive case in some native speakers.
This is my explanation. Anyway, I wonder what case would she employ if she were constructing the sentence without actually using the verb 'potrafisz' in it?
Przede wszystkim bądź wierny sobie, a jeśli nie wkładasz w to ...your heart... to odejdź.