Every time someone tells me to “just do it” they are acting in their own interests and not in mine. I think it is some insidious American plot to reencode reflection as laziness or “procrastination.”
Do not just do it, you will become a cog, someone else’s tool, or a workaholic. Step back and reflect. Or, to rephrase: only just do the things you really want to just do.
I wanted to leave academia after my first job, and stay in that city. I wanted to say no to my first book contract. Those who said “just do it” were referring to staying in academia and then forcing that dishonest book out.
I have a lot of resentment of professors, as you can see. Today I must, must, keep on saying, every fifteen minutes, that I am a competent adult, or the current ones and their ghosts will stampede me.
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In the meeting starting soon, my training says it is a minor issue and I should move for a quick decision, not care what it is, and get back to my real work. Just get it done. The truth is that it is a decision that will have a strong impact, for a long time. Stand back and reflect.
Axé.
coldhearted scientist وداد 
“Just do it” is the Nike theory of life …
It is fine as a reminder to go running for 15 minutes or whatever. It is not fine otherwise.