And -500kcal per day is only 1 pound of weight lost per week.
Gaining weight is easy. Losing weight is very rough.
As someone who went from 105kg to 75kg, I wouldn't describe the process as "rough". It took a series of small, sustainable changes to activity levels and diet over an extended period of time.
At no point did I feel like I was forcing myself to do stuff I didn't want to or was depriving myself of anything.
Couldn't be happier with the results (with how I feel, with the various active pursuits that are now part of my life etc).
So 500kcal per day is only 1 pound gained per week? Sounds like gaining weight is a lot of work! Basically you have to eat 5 large meals for just a single pound? At that rate it will take years of work to go from healthy to obese!
For many, this is not true. My normal activity levels and eating tendencies make gaining weight quite hard for me.