Some things that can make a watch lose
Watch not cleaned and oiled properly.
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 or dirty teeth on wheel or pinion.
Out of beat.
Hairspring not in regulator.
Regulator pins to far apart.
Balance arms bent out.
Loose timing screws.