General Question – Why Must !Important everything?

This is anecdotal, but no less true, in the sense that in the recent past I notice there isn’t a single plugin that I have tried to use and make a custom CSS styling for, that it doesn’t work unless the ‘!important’ tag is put into the end of each style element. Why is this? In the past it was the exception and usually the last thing you thought to try in case some CSS style that wasn’t working as it was supposed to. Now, its the very first thing I try. In fact, at this point, its just a given that !important must be used on any custom CSS style for any plugin, ever, or else the custom style won’t show up. So I just add it by default now. Can anyone tell me why this is?