Toro ended Roma's record of ten consecutive victories with yesterday's 1-1 draw.
"It's a shame, but you can't win them all," De Rossi told Sky Sport Italia.
"After such an extraordinary run it can happen to have a little slip-up and we felt tired towards the end, so weren't as sharp as usual.
"It's particularly a pity considering we dominated the game. Torino just sat back and defended, but we've got to get used to that this season. At least we're still top of the table.
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