If I recall the reason for cursing was they had some major problem cause be a computer overload ... if it was a real landing the mostly likely would of crashed ...
There a reason for dress rehearsals
Stafford fired the explosive bolts holding the descent stage and, moments before the ascent stage engine was to be fired, Snoopy went into a violent spin for around eight seconds until Stafford could bring the craft back under control. Cernan obviously thought they were going to crash and his voice tapes indicate so in what one might charitably interpret from the expletives as something like Oh dear... (The culprit was an incorrectly set Abort Switch, which caused Snoopy to begin a programmed automatic return to Charlie Brown, whilst in a dangerous downward attitude towards the surface).
Heh... yeah, the systems were a bit unforgiving. Stemmed from a turning switch which got turned twice (once by Cernan, again by Stafford).