No clutch or gearbox lasts forever; wear and tear accumulates over time regardless of how careful you are.
Most often, clutch problems are due to the friction and heat produced during operation; typically, the pedal becomes lighter and the clutch begins to slip producing more heat and wear. More sinister symptom,s such as unusual noises or problems releasing the clutch, are not always due to general wear and tear, but can imply a component has malfunctioned, such as a failed bearing or a broken cable.
Gearbox problems usually result from the extreme environment in which they are operated. Components can become worn due to friction and heat, causing clunky gear changes and difficulty finding certain gears. Low fluid levels can also inhibit gearbox performance, particularly in automatic gearboxes
Heat generation is the main component of clutch and gearbox problems. Ensuring the correct oil is used and levels are sufficient can often reduce the wear and tear friction creates. If your clutch or gearbox is behaving unusually, have it checked by a professional to prevent further damage.