A properly made permanent magnet does not wear out by itself. When one loses strength, something in its surroundings caused it, and in most cases the cause is on a short list.
Heat: reversible and permanent loss
Heating weakens a magnet in two ways. Within the grade's limit the loss is reversible: the magnet is weaker while hot and recovers when it cools. Above the limit, part of the loss is permanent and does not come back. The fix is a higher temperature grade and a margin, not just a match to the nominal temperature.
Opposing magnetic fields
A strong field pointing against the magnet's own, such as the current in a motor winding at peak load or another magnet repelling it, can weaken it permanently. This is a common cause of failure in motors, and it is one reason high-temperature, high-coercivity grades are specified there.
Shape matters
For the same material, a thin, flat magnet with large faces is more exposed to demagnetization than a tall, slender one, because its own field works harder against itself. A magnet that sits in a closed steel circuit is better protected than one standing alone in air.
Damage and corrosion
Chips, cracks and rust remove magnetic material. Uncoated or damaged neodymium corrodes in humid air, so the coating must suit the environment. Knocking magnets together during handling is a quick way to chip them.
What helps us prevent it
Tell us the temperature range, whether other magnets or windings are nearby, and how the magnet sits in the assembly. With that we can recommend a grade and a shape that stay stable over the life of the product.