Surely they would be the same thing...?
Nope, not at all.
Say you, Gerard, have a 10% chance of being flamed by me per second. This isn't the same as a 10% chance per year. Say I, the Anonymous Monk, decide to base the flame or not on a die roll. I Take a 10-sided die and roll it, if it comes up a 1, I flame, anything else, I don't (probably should be the other way around ;-)). Now, if I did this once a second and once a year, which scenario results in you having a greater chance of being flamed?