This morning my children asked for a drink of milk. So I told them to get cups out of the cupboard, and I'd pour them one.
My daughter (4) found a short fat cup, and my son (2) grabbed a taller, thinner cup. They put them on the table, and I poured the milk.
My daughter immediately asked why her brother had more milk than her. I tried to explain that they both had the same amount of milk, but it looked as if she had less because her cup was fatter, whereas her brother's cup was thinner. Needless to say, she didn't really understand the explanation (how do you explain fluid volume to a 4 year old?), so I brought the discussion to a hasty halt with my most fatherly "Just drink your darn milk, ok?"
Replace "milk" with "pixels", and it's pretty much the same discussion we have regularly on forums and Facebook ...
"That photographer's images are 300ppi, and mine are only 72ppi! Why are hers bigger?"
They're not. Yours are just as big as hers. Hers are just in a "thinner glass", that's all.
Just take your darn photos, ok?