Why should oil not be too runny or too thick?

Oil should not be too runny or too thick to ensure optimal performance in its intended application. If oil is too runny, it may not provide adequate lubrication or protection for engine components, leading to increased wear and tear. Conversely, if oil is too thick, it can hinder flow and circulation, resulting in poor lubrication and potential overheating. Maintaining the right viscosity is crucial for efficiency and longevity in machinery and engines.