Some things that can make a watch lose 


Watch not cleaned and oiled properly.

Rusty hairspring.

Hands rubbing together, hitting on face, or on the crystal.

Stem not staying in or the watch was left in set mode.

Loose cannon pinion pinion.

Regulator set wrong.

Bent wheel.

Bent or dirty teeth on wheel or pinion.

Damaged jewel.

Worn bushings.

Bent pivot.

Out of beat.

Hairspring not in regulator.

Regulator pins to far apart.

Balance arms bent out.

Loose timing screws.

Mainspring sticking.