"Riding a bike" is an activity. We all have learned how to ride a bike, and the process of learning might be tough, maybe involving scratching, bleeding, and tearing. However, once we learn it. We will never forget it. Thus, we use "like riding a bike" to refer to something once you learn it, and you will never forget how to do it. picture.1

"Riding a bike"是一項活動。我們都曾經學習如何騎腳踏車，過程可能很辛苦，可能會有刮傷、流血或是流淚。然而，一旦你學會了，你便不會忘記如何騎腳踏車。因此，我們使用"like riding a bike"去形容一件事情，只要你學會了，你便不會忘記。