They rebelled because they were aware of the Nazis' true agenda at that point. Regarding its success, I don't think most of the uprising's participants harbored any delusions; after all, the uprising was about "going down fighting," not about surviving. By these measures, it performed remarkably well. Politically engaged Jews, such as Zionists, Communists, Bundists, etc., have been smuggling in firearms and a few other weapons for some years in a secretive and illegal manner. Despite having insufficient supplies to live so long, they managed to fend off the Nazis for many days before they were all slaughtered. That was as successful as it possibly could have been.