Read up on flyback diodes. There are additionally numerous motor driver IC's specifically for this purpose.

A flyback is critical in anything involving a magnetic field, especially a collapsing magnetic field from a motor that stops spinning. The field collapse induces a relatively huge current which will be many many many times greater than anything a normal component is designed for.

Not having one is like driving your car down the highway without any breaks. The only way to stop is to crash.