Denial is just such a hard thing, especially for those unfamiliar with the dynamics of alcoholism. Try as we might to spare those just starting out in the downward spiral from the pain we endured for entire life-long marriages, some people just think they are "different" and that our experience will never be theirs--until it is.
However, once you have lived that life, and learned those lessons, it is much easier to accept the truth of addiction the next time and act more quickly to save yourself from enabling.
I have such a hard time here watching new girlfriends, wives, mothers, and lovers just starting this process, knowing full well that they are going to live in pain until they say "No More" instead of just taking our word for it! Sigh...