I am imagining the words "Man Up" at Thermopylae, hurling a spear at Xerxes.
What does that even mean?
It's the equivalent of 'shut up and get it done.' I partially agree. It's great to think things through, but things have a habit of happening when you are in the act of doing rather than thinking of what to do.
Other interoperable phrases could be
"Toughen up Tinkerbelle"
"Grow a pair, son"
"Who wears the pants in your relationship?"
"Just do it" (proudly swiped from Nike)