In addition to what has been said, instant gratification causes you to want the next thing even faster and easier. This means that over time you get less and less out of each gain and need either larger gains or more of them to be happy. Many MMO's have burned out because they simply can't keep up with the gratification cycle they have instantiated and people get bored/numb. There have been studies, not gonna go find one but there have been several, that prove that people take better care of and feel more pride in objects they worked for than those they were given. I agree there is a tedium point where the reward isn't worth the effort, but little to no effort means a worthless reward. Aim for the middle of that curve and you'll be a much happier person.