Too comfortable leads to disappointment and hurt.
I've been too comfortable in friendship - which often leads to making wise cracks that hurt people's feelings because I've forgotten that words might mean something different to something else than they mean to me.
I've been too comfortable in love - which can lead to hurt feelings when you forget to cherish the moments you have with your loved one. You forget to make someone feel treasured, because you don't think it matters anymore.
I've been too comfortable in my friendly/love relationship with God as well. I think that is what leads to a dry spell in your relationship with God, being so comfortable that you don't worry. I don't worry about spending time alone with God. I don't worry about pleasing him, because I figure I just have forgiveness.
Too comfortable on the couch leads to laziness and obesity. Too comfortable in the sun can lead to skin cancer. Too comfortable can often lead to results that are by no means comfortable.