Once a druid, always a druid. Well, that’s not necessarily true. You can switch up your characters entirely from game to game, and each one will teach you something new. Playing as a Wizard might teach you about mysticism. Playing as a Barbarian will teach you about instinct. Playing as a Druid will teach you about nature. And playing as a Rogue will teach you about how to make your fellow players hate you as much as possible. 

No matter what class you choose, though, each one of them is valid. That’s the great thing about DnD, all have an equal chance of success. Sure, everyone has different skills, knowledge, and instincts, just like everyone in the real world. But they all get the same chance to prove themselves (something that isn’t so true in the real world). It’s all about how you use your advantages to your and your party’s, well, advantage.