How can weaker nucleophiles kick out stronger ones in the reaction of chloroalkanes with sodium iodide in acetone? I have the following SN2 reaction, in an acetone:
1,4-dichlorohexane (1 mol) reacting with NaI (1 mol) to form 4-chloro-1-iodohexane and NaCl.  

However, chloride ions are stronger nucleophiles than iodide ions in an aprotic solvent and iodide ions are weaker bases than chloride ions. Reactions generally form weaker bases, why does this reaction occur? My text shows it does, but I don't understand why. What am I missing?
Acetone is the key here. The solubility of NaI in acetone is about 50 g in 100 mL while NaCl is virtually insoluble in acetone, thus the reaction is driven towards the alkyliodide due to Le Châtelier’s principle, since NaCl will be precipitating from the reaction. This process is called a Finkestein Reaction. Also see this.