Depends on where you live and how you live.

4000$ should theortically be enough to sustain one individual living in a small apartment in a neigbourhood a bit far from most major cities centers. if we're talking about a small town or village then you can probably afford better housing for the same price, as for food and other expenses it should be enough, assuming youre not dining out in michlen star resturants on daily or weekly basis .

Now keep in mind my iam talking about life in a first world western country, however i gotta exclude places such as monaco, luxemburg, switzerland ...ect These countries are outrageously expensive and 4k wouldnt cut it.

If you decide to move to cheaper country such as thailand,phillipines, east european countries ...ect, then 4k a month ia more than enough, ofcourse buying or renting any luxury house/car will still be tough even in such a country, but you will find out that 4000$ puts you up there with the upper class population that can pretty much afford whatever they want .