The clever folds that kept letters secret (opens in new tab)

Why is it difficult to undo, then redo? Obviously one need to be careful (twice) but that's all

I picture it like being more complex than re-folding a street map. It seems a good lot of people mess that up, and it's easy to tell it's happened because some of the folds go the wrong way, and sometimes there are new folds and "puffy" edges that don't belong there.

Just like ironing, where sometimes you see an erroneous V-shaped pleat running down the front of an otherwise impeccable pair of dress pants.