Hearts manager Craig Levein described himself as "not the brightest" and said his side's 5-0 defeat at Celtic was down to him "trying to be clever".
The Scottish Premiership leaders were three goals down at half-time, having lost 3-0 to the same opposition in the League Cup semi-final six days earlier.
And Levein chose to take full responsibility for the humbling defeat.
"I made a decision to try and frustrate Celtic," he said. "But we were far too passive and I got it wrong."
Hearts remain top of the Scottish Premiership, a point clear of Celtic having played a game more than Brendan Rodgers' side.
They beat Celtic in their second league game of this season at Tynecastle, having ended the reigning champions' 69-game unbeaten domestic record at the same venue 11 months ago.
But after playing three games in six days, Levein says he thought a more cautious approach was needed at Celtic Park.
"I thought we wouldn't have the energy to go after Celtic for 90 minutes," Levein told BBC Scotland.. "I should've had more trust in them and let them go after Celtic.
"We spoke at half-time about going back to the way we usually play against them, but it is much more difficult to do on the bigger pitch.
"To be fair to them, they ran their socks off and put in a much better performance. Rather than try to be clever next time, I'll just leave it as is. It's my fault, I apologise to the supporters."
Levein has had several injuries to key players, with defenders Christophe Berra and John Souttar out long-term, while strikers Steven Naismith and Uche Ikpeazu also face lengthy spells on the sidelines.
That being so, the former Scotland manager says he is "thrilled" with the position his side find themselves in.
"If we can get through to the winter break and still be top of the league I'll be absolutely thrilled," he said.
"We get a lot of players back starting in December, and into January we've got another four or five injuries that'll clear up and get [Czech striker] David Vanecek in January on a pre-contract.
"So we'll have much more strength-in-depth come the winter break."