Wow. That’s a toughie. I don’t think I’ve ever quite learned this skill.
verb [ trans. ]
• provide (someone) with a motive for doing something : he was primarily motivated by the desire for profit.
• stimulate (someone's) interest in or enthusiasm for doing something : I'm going to motivate kids to study civics.
Let’s take the first one:
“Provide (someone) with a motive for doing something.”
Alright, I do have a couple of motives for writing.