I can also give another example:
In LoL, games usually take 30-45min, sometimes they take more than 70min though. Planning 70min ahead might be hard, and dinner could go from not even being planned to be finished in that time. And then the game punish you for leaving a game. And it's quite offensive to not come to dinner when some1 else made it for you. That's the kind of problem I see. It encourages bad time managment.
Also, once again I probably worded myself bad. It's not like my grades are low, they are mainly B's - but they could be A's.