Sometimes, mathematicians have to take advantage of the SYMMETRY of a system. Those symmetries can take very complicated forms, but in this case it is very simple. Let's consider a similar but different example.
Suppose I asked you what the next term in THIS sequence would be:
enoone, owttwo, eerhtthree,.....
You would first want to notice that the left and right halves of each of these character strings is the reflection of the other half. If this continues to be true for the whole sequence, that means that there is redundant information. In other words, if I told you the RIGHT half of the next term, you'd automatically know what the whole term is (because you could just make a copy of it, reverse the order, and glue the two halves together to get the whole.)
Basically, this means we can IGNORE the left halves. Then the series becomes something recognizable: one, two, three,... Now we know what the next term in the series will be. It will be "ruoffour" because that is the symmetric string whose right half is the word "four".
What about the M Heart 8 sequence? If you look at just the right halves, you get something that is SUPPOSED to look like: "1, 2, 3". So, the next term will look like the symmetric symbol whose right half is "4"!
I hope that helps,