"I eat vegetables so I am strong."
Translation:Jem warzywa, więc jestem silna.
because silny is adjective for masculine nouns and silna for feminine nouns. In this sentence, the "noun" described is "I". and the person speaking may identify with masculine or feminine gender. You use the form you use for yourself.
The same thing is with singular you sentences and to a lesser degree plural we and you. You need to know gender of the person you are talking to.