You know, Arven could have saved everyone a lot of trouble if, instead of telling you he needed the Herba Mystica for picnics or whatever, he just immediately came out and said "hey, my dog is sick and only these five One Weird Tricks* will cure him, can you help me collect them?"
In what possible universe is that at all a shameful motivation? Why does he hide it until you've collected like three herbs already? Inquiring minds want to know.
*doctors hate them!