Success is defined by the goals you set for your startup. Some people may create a startup in hopes to match their current salary at their "real job", so that

Success is defined by the goals you set for your startup. Some people may create a startup in hopes to match their current salary at their "real job", so that they can quit. Once that goal is attained they consider their venture a success. Others have higher, loftier goals (go IPO) and if they don't achieve that goal then they feel that were unsuccessful and thus continue creating/joining other startups and ventures until that goal is reached. One man's failure is another man's success.