I am pretty sure that ignorance is, in fact bliss.
A person who doesn't know of troubles/suffering etc is bound to be happy.
Also, if that person is unaware of the nature of his/her happiness, they won't bother themselves with questioning it and/or wouldn't really think about the end of their happiess. That is to say, they won't ponder about the happy-to-sad cycles in life, and won't get depressed when they realise that happiess is temporary, because they won't realise it in the first place.

Being aware of happiess can have different effects, depending on the person.
Like for you, mnessie, I think you said that thinkig about happiness while being happy ruis it for you.
Being aware of the origins/nature of my happiness can enhance it.

BTW, about that model of selfish ruin:
I think that acting selfishly requires some knowledge/intelligence/perception capacity, or at least more of it than being naive.
Therefore, a selfish person is probably a bad example of ignorance.(ignorance of what actually)