A question about factors affecting rooting methods

[noodles101]

I have very little knowledge of rooting since i have only owned an android phone for the first time for 2 months now with the s4 and it is miles ahead of what i had before but that's irrelevant just wanted to put my knowledge of the system in perspective. I have a i9500 and I know how to root it but i want to hold of for a while and i was just wondering will i be able to root it even if samsung updates the phone software or a new version of android is releases or will i have to wait for a new method of rooting to work around these updates, basically i want to know what makes a rooting method that worked before become invalid and dangerous to execute?