So, everyone knows the struggle of a string of Christmas lights going out and having to check every bulb until you can find the one single bulb that went out. This happens because Christmas lights are set up in a series circuit. This means that there is only one path for electrons to flow, so if one light goes out, there is no alternate path to get around the one that went out and to the other lights. Putting Christmas lights in a parallel circuit would be more beneficial to buyers because when one light goes out, the other bulbs will still be lit. The reason for this is because in a parallel circuit, electrons are able to avoid the path with the bad bulb and move on to the next. So if you want to be super rich and never have to struggle to find that one bulb that's out, you should invent parallel circuit Christmas lights!