Jose Mourinho was baffled by the paucity of his Internazionale side's display in Sunday's shock 3-1 defeat at mid-table Atalanta.
The former FC Porto and Chelsea manager had no excuses for his team's loss as their lead at the top of the Serie A table was cut to three points.
Inter conceded three goals in the opening 33 minutes and never looked like taking anything from the game despite Zlatan Ibrahimovic's last-gasp consolation goal.
A bemused Mourinho said after the game: "I just cannot explain our first 30 minutes. I am sad and angry.
"I usually like to praise the opposition when my team loses, but this time we played so badly in the first half that I prefer to say we brought this on ourselves.
"I am going to stay quiet and the journalists can use whichever adjectives they like. I could say that they had four shots on goal and netted three, but we just can't give away such ridiculous goals.
"We made too many mistakes and paid for it. However, we cannot forget that we are top of the table at the midway point of the season.
"Perhaps it is time for us to change something about our attitude on the pitch. The inevitable consequence for a team who have made so many mistakes is to change.
"Nonetheless, I am not blaming anyone, I am the face of this side and I am the culprit."