The phrase most often used by participants in this tree!

i'm only a heritage speaker but i'm pretty sure 认真 isn't really used this way?

认真 is diligent, hard working or earnest. This translation is a bit strange. It shouldn't be "serious" but "hard working"

Yeah this is odd. 认真 is closer to "earnest." Or "taking something to heart."

I dont understand the grammar here. Is 的 used to make the adjective 认真 become a noun?

Yes,i am sorry that i broke your favorite cup!