Usually it would be a shrug, unless they give just insane, crazy reasons for quitting. Then it becomes interesting to find out what the problem really is. I've done that with four or five people and as it turned out the root cause for them quitting was not the system, but the theme, GM or the people they were playing it with. They were just in the wrong group for them. For one of those people, he genuinely didn't like the system but he also thought that every RPG under the sun was like Game X. Once he was shown this was not the case, he didn't leave the hobby but just went to look for systems that better suited his playstyle.