Roma's hopes were dealt a blow as they suffered a 1-0 defeat in Turin on Saturday, Medhi Benatia's 18th-minute goal deciding the contest.
Nainggolan played down the impact of the loss, but is keen to avoid repeating the mistake of talking about the title again.
"This is Juventus, they are a strong side. We wanted to press them high, but we should've been more focused," the midfielder told Mediaset Premium.
"Coming here and not taking the chances we create, it becomes difficult to get a point then.
"Talking about the Scudetto was a mistake we made in the past. We must take it one game at a time.
"We have a game in hand against Sampdoria. Losing to Juventus in Turin is not a tragedy, we still have the return match at the Olimpico and can make up lost ground.
"We're doing good work and want to finish as high up the table as possible."