brakes are wearing out very fast, why?
Assuming disc brakes, some reasons for short pad life could be:

Riding conditions - If you're riding in gritty mud, pad life will be shorter than dry conditions.  The mud can form a grinding paste which wears the pads quicker.

Damaged rotors - If your rotors are scored or damaged, this can accelerate pad wear.  If you've worn a pad down to the backing plate this can damage the rotor and lead to shorter pad life.

Not bedding the pads in sufficiently - New pads straight out the packet need bedded in before use.  This typically involves putting them through a few braking cycles to bring them up to a high temperature.  Pads which have not been bedded in, will wear quicker when subjected to wet muddy conditions.

Pad material - Brake pads come in different materials which can have different pad lives depending on usage.  E.g. sintered pads should last longer in muddy conditions than resin pads.  However, some brake discs are not designed for sintered pads.