Armstrong has said he thought he and Aldrin had about a 50% chance of success for the moon landing. Failure could mean lots of things outside of situations resulting in death, but still, they were taking an awe full risk.

Also, looking at the manned Apollo missions, one out of 12 resulted in the death of the crew (Apollo 1), and one in 6 missions were failures (Apollo 1 and 13). Space flight was a hugely risky endeavor back then.