The pink cloud is the illusion that life is going to be all sunshine and flowers once you quit drinking. It's just an illusion, life isn't that way. I think it gets in the way of lasting sobriety because it can be a huge let down when the euphoric feelings go away and that can set you on the path to relapse. I was sober for six months, and the first three were AMAZING. Happiest I've ever been. After Thanksgiving I started to get depressed and I kind of went with it. I relapsed March 1st.
I approached sobriety with great expectations and when it didn't meet them I lost the motivation to work on myself. It didn't take long to get over the chemical dependency, but there was so much more to it than quitting drinking.