Losing weight takes forever, but getting it back is instantaneous!!

When dieting, losing a few hundred grams or 1kg really requires controlling your diet and exercising for several days just to barely make it come off...

It feels so disheartening and gives me a reality check when the numbers on the scale immediately return to their original state just because I let myself eat for a few days during the weekend or holidays!!!

Why is it so hard to lose fat, yet it comes back in an instant? How do you all manage to get through holidays or weekends when maintaining your weight?