What is the meaning of the quote Man will occasionally stumble over the truth but most of the time he will pick himself up and continue on?

It means that people often ignore inconvenient facts or truths , which force them to think about something they take for granted as correct or are sure of something being unquestionably right ,or shake their beliefs or sense of right/wrong . Hence they continue on their old beliefs or moral values as if they never discovered the uncomfortable truth rather than deal with the trouble of re-aligning one's stand or change earlier beliefs.