うん and ます form in the same sentence


<https://twitter.com/MRko_aki___/status/1395581370328489985> A Japanese artist
recently tweeted

> うん、頑張ります

What is the stylistic reason for combining the casual うん with the polite 頑張ります
rather than はい?




To him, perhaps "うん、頑張る" might have sounded too personal, but "はい、頑張ります" might
have sounded too official. This tweet sounds as if he first said うん to himself
to make up his mind, and then said 頑張ります to externally declare his stance. In
other words, he wanted to signal that this was basically a personal tweet, but
at the same time, he was aware that he had to say something externally and
many people would read this.




To him, perhaps "うん、頑張る" might have sounded too personal, but "はい、頑張ります" might
have sounded too official. This tweet sounds as if he first said うん to himself
to make up his mind, and then said 頑張ります to externally declare his stance. In
other words, he wanted to signal that this was basically a personal tweet, but
at the same time, he was aware that he had to say something externally and
many people would read this.

