My thoughts on Math Theory

Some people feel as though math theory is completely useless. “Why bother to prove all those math theories?” seems to be their “practical” viewpoint.
I, however, like to know that when I am doing calculus or trig or geometry, the steps and theorems that I envoke have actually been shown to work 100% of the time. And I know this because they have been proved using math theory. I mean, the things you do with calc and trig and geometry can be pretty important. Wouldn’t it suck if you suddenly stumbled upon the exception that proved a theory was incorrect?