People are more motivated as they get closer to the goal - when implementing a process indicator, the process could be highlighted e.g. as some special success. As well, a process step indicator can be handy to show the users, how many forms are yet to fill in (+ estimated time left)
People are more motivated by intrinsic than by extrinsic rewards - intrinsic rewards (autonomy, lerning, mastery, meaning,...) are more about feelings and liberties of the individuals, while extrinsic rewards (badges, money, points) are controlled by external factors. Real-life example: That's why slot
machines are not necessarily about the loss or outcome of money but even more: The user wants to get better and better in the game (intrinsic
rewards), while getting incentivized by external factors such as badges, points and money. And as so many factors come together here, the loss of money is not perceived as being that tragic.
People are motivated by doing things on their own in an autonomous way. To encourage this aspect, as a designer we can give our users the feeling of them being in control of the current task and will reach their goal without any effort or assistance needed.
E.g.: The newly released movie "Black Mirror - Bandersnatch" implements
the user and his decisions within the movie, so the user can decide
about which path the movie takes. But beware: The overuse of guidance in ground up intuitive process can already lead to less motivated users.