The "Blowing Into Cartridges" legend is an urban legend revolving around the Nintendo Entertainment System, as well as the Super Nintendo Entertainment System and the Nintendo 64.
Description
According to the rumor, blowing air into the inside of a video game cartridge would clear out the dust inside that allegedly caused games to glitch up or not read correctly. Part of this reason this myth has persisted for decades is that many players have anecdotal experiences of games working as they should after being blown into. Aside from this, the practice, to many, just intuitively feels like something that should work.
And why did it work? Blowing into video game cartridges has a noticeable impact on games working correctly. In fact, the moisture that enters the cartridges in our breath has saliva in it. This will conduct electricity a lot better, creating a stronger connection. The blowing also removed debris. But nintendo advised not to do this, because it can actually damage the games in the long run. [1]
The reference below is outdated and wrong.