New to plants!

I’m new to plants and RAPIDLY developing an addiction lol. I’m having fun water propagating and starting them off from other plants. I chopped this from my dad’s plant yesterday.. but what’s up with this brown-ish leaf??

I’m new to plants and RAPIDLY developing an addiction lol. I’m having fun water propagating and starting them off from other plants. I chopped this from my dad’s plant yesterday.. but what’s up with this brown-ish leaf??