First of all, I adore Mary Oliver's work! Secondly, I agree with all that you've said. I've been a life coach for over 15 years and you are exactly right that it is only when people get serious, and authentically motivated that they get stuff done -but then they can get all kinds of things done (as you are a great example of).
One of the things I do is to help people make a plan to go after what they want, including looking at how they might be part of what is standing in their own way. Then we make a back-up plan, and maybe another back-up after that because force of will isn't always going to get you where you want to go. Sometimes you need to try another route or evaluate why things didn't work out the first time and tweak the plan. This takes intention, effort, and resilience - it's work, which is often messy and difficult (which is why they hire someone like me to help them go there with them.)
It also takes intensive self-reflection and analysis of how you yourself are contributing to the problem or standing in your own way - often because of stories you have internalized as a child. Starting to recognize them as stories and not "the truth" opens up a lot of possibilities. The chinks in the armor are where the doubt and disempowering narratives take hold, so regularly working on repairing the integrity of your "suit" is necessary and you never "arrive" - there is always work to be done on the self in order to lead a full life and truly meaningful life.
I realize this is preaching to the choir here, but since this is one of my favorite topics, I just had to riff a little bit. Thanks for inviting me to the conversation and rock on!