From Jeffrey Polet:
The idea is strange at its core. You pour water on your head in order to avoid donating, but more than that, you do it in a very public way. While the challenge may have the tertiary benefit of drawing attention to the disease, what it really draws attention to is the self. This is why it’s an effective approach in the age of social media, the major advantage of which is self-promotion.
The chain effect operates essentially on the principle of shame. “I have performed this good deed, and I challenge you to do likewise, and if you don’t, everyone will know.” It has the scent about it of a kind of mass hysteria: people engage in the act because it seems good, without having to do an actual good deed, or think seriously about the consequences. Attributing motivation to any human action is often tricky, and rarely are motivations pure in the sense they are absolutely good or absolutely bad. Generally speaking, any action has about it a hint or a tint of self-interest.
But that self-interest is simultaneously heightened and occluded by the complexities placed upon action by publicizing and pressuring. To resist the highly-publicized demand to pour water on oneself is to draw attention to the fact that there is some sort of serious deficit in your character. What kind of person doesn’t want to rid the world of ALS, or of evil altogether?