When a person feels that things are going smoothly,
that he has no difficulty in getting up in the morning to pray,
to recite blessings over food,
to set aside adequate time for Torah study;
when he feels that there are no obstacles on his road to holiness
–this is a clear sign that he is lost, that nothing can prevent his descent into hell.
That is an unmistakable marker that if he wishes to save himself, he must immediately rise and commit himself to drastic action.
From Understanding the Tanya, Chapter 35, p. 189, by Rabbi Adin Steinsaltz