He saved Gemini 8 from near-disaster due to a stuck thruster during the first ever US docking in space (with an Agena target satellite). He nursed an X-15 in after a test flight went wrong, setting a record along the way for the longest X-15 flight in the entire program (it bounced off the top of the stratosphere during re-entry and had to glide about a hundred miles further than normal to make the airfield). He was the LLTV test pilot -- the LLTV was the turbofan-powered test bed for the Lunar Excursion Module's descent control systems -- and survived an engine failure at low altitude, ejecting about 0.5 seconds before it became non-recoverable.

His list of hair-raising flight test achievements is remarkable; he was basically the best test pilot in the astronaut program for making split-second decisions when the shit hit the fan, and he'd also been the test pilot for the lunar lander. Do you need any more?

Start reading here:

https://en.wikipedia.org/wiki/Neil_Armstrong

And pay attention to the stuff before Apollo 11.