That just because Destiny is not like any other game out there. Destiny is p2p game so there are no servers for hosting. The things you need your friend to look at are: Jitter, ping, packet loss, up/down speed, nat type. There are tests available online that your friend can use to check his connection. Also, don't ever use wireless connection with Destiny, wired is the correct way for Destiny. Look through the network trouble shooting guide. Contact the isp while playing destiny and see if there is any problems.