This video from Enterprise Gamification Consultancy nicely illustrates how extrinsic motivators can be initially powerful (if relevant and genuinely rewarding) but often ineffectual over time. That said, I’m not entirely sold on their explanation of intrinsic motivation. Whilst their squirrel-chasing analogy succeeds in demonstrating that interest is a driving force of intrinsic motivation, it fails to explain that internally-rewarding things like mastery, capacity analysis and higher-level knowledge acquisition are vital components behind intrinsic motivation.
Once Rupert realises that he cannot make any progress on the squirrel, he will learn** that any change in effort would be futile. Rupert will thus never be able to track his progress (or lack thereof) in attaining squirrel-chasing mastery, meaning his intrinsic motivation will wane and he will stop performing the desired behaviour.
**Assuming that Rupert the dog has human-like capabilities for reasoning and learning.