Why is a bike difficult to ride if it needs oiling?

A bike can be difficult to ride if it needs oiling because the lack of lubrication in the chain and moving parts causes increased friction. This friction makes pedaling harder and can lead to stiff or unresponsive gears. Additionally, rust or dirt buildup can occur without proper lubrication, further hindering performance and making the ride less smooth and enjoyable. Regular oiling ensures that parts move freely and efficiently, enhancing overall ride quality.