Why did Doon trade with Lina?

Could you please elaborate on the reasons behind Doon's decision to engage in a trade with Lina? Were there specific benefits or motivations that drove Doon to make this choice? Additionally, was there any particular asset or service that Lina possessed that Doon was seeking to acquire through the trade? It would be insightful to understand the dynamics of this transaction and the factors that influenced Doon's decision-making process.