Things are what they are.
Everything acts according to its nature.
Nothing escapes its own nature.
In mathematics, "A=A" is a useful tautology, principle, or definition, because mathematics is a pure language, having no concrete referants, and 'A' can be intensionally defined and then known with absolute certainty to be nothing more than what is given in that definition.
In life, however, "things are what they are" is a semantically null grammatical formulation, imparting no informational content. Intensional definitions of real-life subjects can easily fool one into thinking that by defining something (applying a label to it), everything worth saying about that thing has been summed up in one neat little idea--this is dangerous, because one can never say all there is to say, or know all there is to know, about any concrete subject.
Having said that, I have a quasi-deterministic view of life--I allow for the possibility of quantum indeterminancies as mentioned by JWood, but these don't somehow magically produce free-will, nor do they necessarily imply uncaused or truly random behavior at the quantum level, but merely behavior far beyond our current ability to predict. So, free will does seem to be a mere illusion, but one that is necessary to human existence. When I first realized the logic of the deterministic argument, I went through an existential crisis and in fact a depression--but finally, I realized that existentially, one has to simultaneously accept (logically) the implications of determinism while irrationally and existentially saying essentially "Yeah, I don't really have free-will, but I think I do, and everyone else does too, so fuck it--that's good enough." This was to prevent my brain locking up and rendering me mentally and physically catatonic. And it's not like we're all tools of some outside consciousness or will who's moving us around like puppets--we're just little clockwork people who think (on some level) that our thoughts and decisions are immune to the laws of physics. We're still capable of feeling and enjoying life and believing we have free-will, so we might as well have a good time of it.
Also, I believe the "Determinism versus Free-will" debate gives a false-dichotomy, or, at best, one against which far too many people have a very violent knee-jerk reaction because there's no way in hell you'll get them to admit they don't have free-will, therefore all logical reasoning is out the window before the debate is underway. I think instead the concept of determinism should rightfully be balanced against the concept of "uncaused events," which in and of itself is one of the most hilarious and nonsensical concepts I've ever come across. After you've gotten them to realize that determinism makes sense--because uncaused events don't--then you add "Oh, and by the way, that means you have no free will."