People aren’t very good at judging changes in size. For example, I’ve found in my research with colleagues that when you make something bigger, people routinely underestimate how much bigger it is. This happens because, when estimating the volume of objects, we visually add instead of multiplying the changes in height, width, and length. So although increasing the height, width, and length of any object by 26% is enough to double its volume (because (1.26)3=2), to our eyes it will only look around 78% bigger (or 26%x3).