The fact that you don't need a force for it to move forever at a given speed in a given direction, that's not obvious, because in daily life you don't see that.

对于物体不需要力的作用就能保持,确定的速度和方向持续运动这一事实,它并非显而易见,因为在日常生活中你看不到这种情况

耶鲁公开课 - 基础物理课程节选