The best dialogue to develop both characters for readers is:
"I don't know," Marco said slowly, "Are you sure we'll even get tickets? This is going to be a pretty big deal."
"I hope my uncle can get us tickets," Sadie said. "I know I'm an optimist, but it could be really hard because the band is so popular."
"Well, I'm usually skeptical and I still think we have a good chance," Marco said.
"We're going to have so much fun," Sadie said. "I bet we'll get to meet the band. I bet we'll even get to hang out with them!"
"We probably won't even get to go," Marco said. "I bet the whole show will get canceled and we'll have a terrible day."
This exchange effectively illustrates Sadie's optimism and enthusiasm contrasted with Marco's skepticism. Sadie's persistent hopefulness about the event showcases her character as someone who focuses on the bright side, while Marco's reluctance to believe things will work out reinforces his skeptical nature. Additionally, their back-and-forth dialogue highlights their dynamic friendship, allowing readers to see how they balance each other's perspectives.