Nanu be giving Ash the third degree we’ve all been wanting for years

He’s not even playing hardball here really, just spouting some (likely intentionally) stock “bad person” lines about friendship holding you back and such. A fitting test for a dark-type specialist to give young trainers: “Can you handle a bit of hardship and negativity, or will you let your anger and insecurity get the best of you and potentially get yourself and your Pokemon hurt?”