Tony,

Two years is just a bench mark. It's an arbitrary date set out in the future that says if you have made it this far you stand a better chance of no reoccurance.

Its a fairly meaningless date as we all plan on making it two years at the very least.

Simply put, every day you put behind you lowers your chance of a reoccurance, and the more of thaos days you can string together, the better your chances on no reocurane.