It's not at all difficult if you are eating junk food. For example a single Medium Pizza alone is enough to fill your entire day's worth of calories.

I know because I've experimented with this when I started measuring my weight, heck sometimes having a single Wendy's Baconator will not only fill your entire calories but even make you gain weight.

Your activity levels of course also matter but I'm assuming sedentary lifestyle.

This is much more different for healthy foods however.