Can Do It Cream was a "special magic cream" that Papa Smurf had offered Weakling in the episode "A Little Smurf Confidence" that he told the young Smurf would give magical strength to the one wearing it. Eager to try it for himself, Weakling applied it on his nose and soon found himself being able to do things that he wasn't able to do before, even in rescuing his fellow Smurfs from danger when a storm had caused the bridge over the River Smurf to collapse. However, Papa Smurf revealed to Weakling that what he was wearing all the time was smurfberry jam, showing that there really was no magic involved and that everything Weakling did was because he believed in himself.
A similar placebo was also used in the comic book story "The Olympic Smurfs".