Engine wear is inevitable, but can be reduced to the point of being almost unimportant. Wear is caused when various parts rub against one another. The trick is to separate these parts with barriers of lubrication; as long as the metal parts do not touch one another, they won't wear. A thin film of oil between moving parts (such as piston rings and cylinder walls) prevents the normal microscopic welding and tearing these metals experience when forcefully rubbed together without the barrier of oil.
Most engine wear occurs during startup when those piston rings and cylinders may have a too-thin film of oil to prevent high spots from rubbing and wearing. As soon as the film of oil thickens enough to separate all the parts, wear essentially stops. The oil film thickens due to its being dragged between the moving parts by it own internal friction (viscosity).
In the case of plain bearings, like the bushings supporting transmission shafts or camshafts, the parts are separated after about 12 degrees of shaft rotation.
The smoother and more accurate the surfaces, the thinner the oil film can be. Improved finishes and more accurately machined parts are the main reason today's engines can use thinner oil. Thicker oil is needed for the rougher parts of older motorcycle. It is therefore important that you follow the manufacturers specifications of the engine oil.