What are “attachments” and how do they hinder my spiritual life? Part I of II

What are “attachments” and how do they hinder my spiritual life? Part I of II: In your recent series on getting stuck in spiritual growth (which was very helpful  by the way) you mentioned the idea of “attachments.” I think I understand this as I have read a bit of St. John of the Cross. However, I would be grateful if you could help me understand it a bit better …