Are you a "move away" or a "move towards"?
You've heard of optimists and pessimists. A slightly more complex way to look at a similar trait is that people tend to fall into one of two categories - that of "move away" and "move towards". A "move away" person is someone that is motivated by moving away from something they do not like or fear. A "move towards" person is someone that is motivated to move towards a particular goal - something they want. It is neither good nor bad to be one or the other. It just 'is' - and it takes all kinds to make up a world. The key here is to first figure out what your mentee/employee is and to frame assignments, milestones, objectives, etc. in a way that motivates them depending on which category they fall into.
A simple way to find out which way someone leans is to ask them what they did over the past weekend. If you get a narrative along the lines of Person A: "I finally cleaned up my house this weekend. I can't stand clutter. Also got to take the dog to the vet and got him his shots so he doesn't get sick" then you have a 'move away' person. This person is charged up by focusing on things they want to change and they act on that.
If the person's narrative sounded more like Person B: "Got my house all nice and clean - gotta be ready to have people over. Took my dog to the vet to keep him healthy and safe" then you've got a different twist on essentially the same activities. However this person likes a clean house to be ready for guests (move towards) as opposed to hating clutter (move away). Person A doesn't want their dog to get sick (move away) so they take them to the vet whereas Person B wants their dog healthy (move towards) so they do the same thing but describe the motivation differently.
Now that you have this assessment in hand let's see how to apply it. Say I had an assignment to build out a company website. I would assign this same project differently to a move towards person than a move away person. To a move away person I'd say something like "we need a new website built. All our competition has snazzy websites and I'm concerned if we don't have one ourselves we'll be in big trouble. The company might lose out to the competition and close down." On the other hand to a move towards person I'd say instead "We need a new website. A presence on the web is a very important and this is a very visible project for yourself and the company." For the move away person I give them consequences they'll avoid by succeeding on the project. For the move towards person I give them benefits of the project - something to shoot for.
Once you start noticing what makes different people tick and start to phrase your communication in a way that targets their motivational engine you might be amazed at what a constructive force you have at hand.
So what are you? Move away or move towards? Once you've figured that out then go and figure out what your partner/parents/siblings/friends/boss/employees etc. are. Good luck!