Did doing this actually help at all? If so, how?
Popular belief among those of us who remember the original NES held that that blowing into an NES cartridge removed dust from the contacts, which allowed a better connection to the system. In practice, the method was similar to the following:
- Plug in cartridge, turn on system
- Curse when system does not work
- Pull out cartridge, blow
- Re-seat cartridge, try system again
In a few cases, blowing may have actually removed dust, but the truth is that most of the time, what actually fixed the problem was the act of pulling the cartridge out and putting it back in.
As the original NES required you to put the cartridge in and then down, another common trick was to shove a second cartridge in the slot on top of the first one, which prevented the bottom (game) cartridge from slipping.
Finally, Mental Floss has a detail analysis of the effects of blowing in an NES cartridge.
For the most part, it didn't do anything. When the system didn't work, most people's natural assumption was that the connectors were dirty. The most logical way to clean something like cartridge connectors was to blow on it. They also sold cleaning kits, but in my experience they weren't actually that helpful.
The problem wasn't the cartridges, but the connectors in the NES itself. According to Wikipedia, the problem is due to Nintendo's use of a "zero-insertion force" cartridge connector:
When a user inserted the cartridge into the NES, the force of pressing the cartridge down and into place bent the contact pins slightly, as well as pressing the cartridge’s ROM board back into the cartridge itself. Repeated insertion and removal of cartridges caused the pins to wear out relatively quickly and the ZIF design proved far more prone to interference by dirt and dust than an industry-standard card edge connector. Exacerbating the problem was Nintendo’s choice of materials; the slot connector that the cartridge was actually inserted into was highly prone to corrosion.
Further, Nintendo used the "10NES" lockout chip, which required constant communication with the cartridge to authenticate it as a legal cartridge. When it didn't have the communication, the result was "the blinking red power light, in which the system appears to turn itself on and off repeatedly because the 10NES would reset the console once per second. ... Alternatively, the console would turn on but only show a solid white, gray, or green screen."
Only a few years ago I was playing on a NES and discovered the cartridges would work best when barely inserted, just enough to clear when pressed down (this after I had cleaned the contacts). This was quite contrary to my strategies as a young kid. I was applauded for determining the "trick"; it seems my methods are more methodical these days.
So perhaps it was the reinsertion that did it and not blowing, specifically: inserting it less. I'd be interested to know how many other NES consoles had this idiosyncrasy.
NES cartridges physically attached to the console - similar to USB drive. If dust got in the cartridge, it could get between the contacts on the cartridge and contacts on the console, preventing a good electrical connection.
Blowing into the cartridge can shift the dust away from the contacts, making a non-working cartridge functional again.
Not only did word spread around, but a lot of media outlets showed kids blowing on the cartridge to make it work. Nintendo Power in particular would recommend it, as well as the official Nintendo Cleaning Kit, and it was well-known that dust was problematic.
Like every other answer here though, I have to point out that re-inserting the cartridge was what really did the trick.
I admit that I also blew into the console itself because of this voodoo, because if dust could get into the cartridge, why not the system? It was about as effective as cartridge-blowing.
My brother and I did this all the time with our old nes. Beyond blowing out the dust there seemed to be some connection with moisture. If I blew it out and then breathed on it to make it damp it seemed to work better.
The question about how everyone knew to do it? I agree with the instinct theory. My brother and I worked out this system by ourselves. You look at it, and for some reason the first thing you think of is either to stick your finger in it or to blow in it, LOL.
I did an experiment back in the day with an Atari 2600.
When inserting a game I would randomly choose, by coin flip, one of two things.
- Use some rubbing alcohol and a cotton swab to clean the cartridges contacts.
- Lick a cotton swab and clean the contacts with that.
Then record the success rate of the game starting on first insert.
I didn't keep the results but I do remember that by a very large margin the lick and clean beat the rubbing alcohol method. So I surmised that it was the saliva that did the trick. When other game systems came out I also assumed it was the moister in the breath that came out when blowing that helped and not any cleaning effects.