The tea bag was an accidental invention.
In 1908, New York tea merchant Thomas Sullivan sent samples of tea leaves to some of his customers in small silken bags. Many of the recipients assumed that the bags were supposed to be used in the same way as the metal infusers. So, they put the entire bag into the teapot, rather than emptying out its contents.
After such positive feedback from the happy accident, Sullivan designed intentional teabags for commercial production. In the 1920s, his sachets made of gauze—and later, paper—included the string with the tag hanging over the side so the bag could be easily removed.