The hosts surged ahead through Tom Hateley's 10th-minute opener and a Jamie Murphy effort and although Jonny Hayes halved the deficit for the Dons, further goals from Murphy and Michael Higdon put the result beyond doubt.
"I didn't feel we were outplayed, Motherwell are probably the best team out with Celtic and we don't like losing to them - and we haven't in the last three times we played them," said Brown.
"All of the credit should go to Motherwell for the way they played. If we don't take the chances we have, then we won't win the match.
"I'm not clutching at straws, I have told the players that it was an unacceptable result and the humility in the dressing room is there to be seen.
"The Christmas message is humility in the performance and determination to banish the disappointment in our next fixture with Dundee."
Aberdeen could have drawn level on points with Stuart McCall's side by recording victory, and now sit in fifth some 10 points adrift of SPL leaders Celtic.