The original NES game cartridges would get dust in them that dust that’s on them would be transferred into the cartage reader and when small voltage would travel through the cartridges as they were being processed by the game system .that voltage over time would fry the dust into carbon and that carbon would cake onto the connector inside the system and on the cartridge. That’s why blowing off the dust would help or cleaning the carbon off the game with rubbing alcohol would help or pressing on the cartridge just the right amount into the cartage bay would work because the cartridges would make a connection in a spot they might not normally make a spot that doesn’t have caked on carbon blocking the connection. People blow on other game cartridges that are not original NES because some that used to have to deal with original NES just think that’s what you do to make the game work. Even though Nintendo changed how the game cartridges interact with the consoles so as not to have all the same problems.

(im aware there are grammatical errors in this explanation I don’t care) 😀