Originally Posted by Talith PA
Just because it is possible for him to build up a tear into muramana before the game ends doesn't mean it's worth it. If for some reason you feel like you need magical damage and don't mind the significant build up time then by all means.
Personally, the statistics you sacrifice by purchasing an early tear and the amount of time it takes to build up stacks is not worth the end result, especially when considering the opportunity cost of other items while you are working on it.
Last season, Urgot was literally unplayed. This was because the accepted norm was building tear on Urgot, which made his early game weaker. M5 then popularised the Bruta/Glacial build which made him really overpowered, to the point where he later got nerfed pretty hard. Although I assume that muramana actually has some high level synergy when you go full mana tank but that's a different story!
Point is, Tear is a 700 gold investment for no immediate benefit, at a point in the game where 700 gold in AD or Armor can make you completely dominate the lane.