A little boy was given an instruction by his Dad to be arranging his room everyday, whenever he's out. The boy adhere to it and makes sure his Dad's room is always neat before he returns. Each time his Dad gets back from work, he praises and thank him for the wonderful work he did. This enlightens and encourages the little boy, he never would want to miss a day without taking care of his Dad's room.
The boy's father got used to him arranging his room and stopped thanking him. The little boy feels bad each day his father comes back from work and wouldn't make any compliment about what he did.
The father came back one day, stressed up, only to find his room unkempt, he overlooked cause he thought his son was busy the whole day. He discovered the same thing, the next day and decided to call the son and scolded him for not doing what he asked him to do.
The son had to speak up and told his Dad that he's no more appreciating what he does and doesn't gives him the urge to do more! The father realized his mistake and promised to continue encouraging him.
PS: Never stop appreciating. Yes! It may be something that's done for you regularly and may not see the need to say "Thank You" again. It would only serve as discouragement to the person helping.
No matter how little is done, it's worth thanking