Psychological warfare is about the fact that one of Renekton's biggest strength is that enemies love to focus him down. This is good because he can soak up damage away from the carries. If you just tank Renekton then smart people will know better and not focus you as much. Too much damage and you will get focused down to quickly. By having stack items it increases the aggro that you will receive. With his ulti, guardian angel, and his aoe attacks, Renekton with will get 20 stacks very quickly and with the extra moment speed becomes almost impossible to kill. However he will inflict tons of damage and keep aggro off of carries. You can do almost the same with a bloodthirster but it costs WAY more and lifesteal isnt as good as speed in my opinion for survival and positioning, especially when Renektons ulti depends so much on positioning. I find that i can carry games a ton with renkton, but beware garens complex, of stealing kills from your team mates. So many times have i seen a Renekton with 20+ kills and still lose the game cause the team has none.

Your stun is most important, max it first always. The synergy with phage means no escape for anyone who stumbles across your path.