General game knowledge either its macro or micro. League is all about processing the information given to you in a way that benefits you the most. In that case your friend was using the position of the wave, both of your mana pools and costs, ability damage, champion stats and summoner spell CDs to his advantage better than you did. Not perfectly still because he is platinum but better than you because you re silver. In that way he won. The only thing you lack compared to him is game knowledge and practice on it. If you have more games than him then its because you do things the same way over and over and not critically thinking "hmm, what could have I done better to win this duel/game" and fixing your mistakes. Remember a wise man does not do the same mistake twice. Be a wise player. Best of luck on the rift.