How to influence people to work in your favor

Very recently I had an experience that would make me say “how I influenced someone to work in my favor”. An ideal flat mate of mine (…read a pukka teetotaler with no drinking, smoking or tea sipping habits) who had been chiding me for quite some time for my occasional drinking sprees and who had vowed never to touch drinks in his life had actually went to the liquor shop and got a bottle of whisky for me. I had only said to him that he lacked guts to do so and he would be laughed at if he joins the armed services and said no to drinking (no offence meant for those who do not drink in spite of being in the armed forces. This guy is actually planning to be in this profession). This was not the only thing. I actually had to remind him again n again what I had already said. Continuous pestering is always needed to get something actually if u don’t get it easily. “Zidd karo…Duniya badlo” as the good old wording of Dainik Jagran says….does seem to be true leave aside whether it’s a right or a wrong reason.
The epilogue has been that he has vowed once again not to bring liquor again in his life for someone…and it has given me another challenge to prove him wrong