I've been "chubby"
most of my life. Until the age of 5 or so, I was skinny as a bean pole (and I have the pictures to prove it), then I blossomed out, so to speak. I've been 250-300lbs+ for the past 20-25 years. It's not something that's easy to change. You can't just look at someone who's fat, and assume it's because they pig out all the time or are lazy.
It's not even that I eat a lot (I tend to snack, more than anything), and I enjoy walking (I'll go 30-40 minutes or more one way, then come back). I don't do it as often as I'd like or should, but I do. It's only the past few months that I've begun to lose some weight. Not really sure when it started or why, but I've gone from 310-320, down to under 290. Could be my last job (was really stressing me out). Still, I'm not complaining.