This is scarcity thinking, to be blunt. You should never make less than $150 for anything you write for others. Let’s think like a pro: How many words was the post? How long did it take you? How much did you make per word or hour? How much time did you put into pitching it, back and forth regarding content, etc.? If you want to make a living as a writer, don’t focus on motivation, focus on where the next project comes from, on how you can leverage this one into a steady stream, how to build relationships. And please don’t start thinking about selling advice when you don’t have the experience to back it up. You don’t get to call yourself a marketer until you have made money for your clients in measurable ways and they acknowledge it. Brutal? No, real world. I’m happy you made $150. Now you have to do that ten times a week every week. Then write about it.