My personal experience using Lua/love2d for some (amateur/hobbyist) game programming is that the adjustment really wasn't too difficult at all -- I've run into an off-by-one error or two, but not at any greater (or reduced) frequency compared to 0-indexed languages AFAICT. Obviously, some of the sibling comments here disagree, so the only reasonable conclusion I can draw is that it varies from person to person how much they care and how much effort it takes to adjust.

At the end of the day, like all language design decisions involving an arbitrary choice among reasonable options, you get used to it once you use the language enough (and also some folks will refuse to ever use the language because of it for aesthetic reasons).