a × b = b × a
Most people speak about this as if it is common sense.
For example, let's say 265 * 7948 = 7948 * 265. I can't get my head around when arbitrarily putting this adding 7948, 265 times, is equivalent to, adding 265, 7948 times.
(I never understood this until I visualized it in a table format.)
I asked similar questions to many people and almost all of them replied as if it were a weird question, like "What is there to question about it, ab=ba? We know it ..blah blah blah."