Luffy wants to go to Laughtale. Zoro wants to beat Mihawk and so on. Those dreams are somewhat precise. Chopper's dream is to cure all illnesses. How would you even do that? There are too many illnesses out there and new ones constantly develope.
Back to Zoro's dream. He wants to become the strongest swordsman. He wants to prove that not by cutting down every swordsman, just the one recognized as the strongest. So if Chopper is able to cure the hardest to cure disease, he would have proven that he could cure all diesease. But what is the most difficult to treat illness? What is Chopper's Mihawk?
Perhaps the disease Roger suffered from. He knew he had only 1 year left and achieved great things during that time. With all the parallels between Luffy and Roger, Luffy will get the same disease. Many people think Law will give him eternal youth and cure it that way. But no, Chopper will cure that disease around the same time that the other Strawhats achieve their goals.
All the other Strawhats will also achieve their goals around the time when Luffy becomes Pirate King. Brook for example wants to see Laboon. The disease killed Roger shortly after he became Pirate King. Maybe it will be the same with Luffy. So Chopper has to accomplish it also at that time.
Back to Zoro's dream. He wants to become the strongest swordsman. He wants to prove that not by cutting down every swordsman, just the one recognized as the strongest. So if Chopper is able to cure the hardest to cure disease, he would have proven that he could cure all diesease. But what is the most difficult to treat illness? What is Chopper's Mihawk?
Perhaps the disease Roger suffered from. He knew he had only 1 year left and achieved great things during that time. With all the parallels between Luffy and Roger, Luffy will get the same disease. Many people think Law will give him eternal youth and cure it that way. But no, Chopper will cure that disease around the same time that the other Strawhats achieve their goals.
All the other Strawhats will also achieve their goals around the time when Luffy becomes Pirate King. Brook for example wants to see Laboon. The disease killed Roger shortly after he became Pirate King. Maybe it will be the same with Luffy. So Chopper has to accomplish it also at that time.