By stating that he and Anna are "incongruously matched," Jack meant that he and Anna have a lot in common and that's what makes them not fully understand each other.
In summary, we can say that Jack recognizes that he and Anna are very similar, but that they have specific differences and that they stand out in a way that makes them equally different. These differences and similarities make them combine strangely but efficiently.
This question refers to a letter that Jack wrote to Anna, his fiancée.
More information about letters in the link below:
https://brainly.com/question/13116029
