It's why we make goat noises at people who claim their bachelor's degree in engineering has led them to come up with a Theory of Everything. You have to know a lot before you can even know what is missing, much less how to fill the gaps.
Some of this awkwardness is because, while science is libertarian - it requires freedom and breaking rules - peer review is staunchly conservative. Established ideas are therefore difficult to overturn and, until it is replicated, contradictory data is often dismissed as anomalous. Yet, there are some concepts which are considered so rock solid that it is difficult to imagine them ever being replaced with something better. What's more, these concepts have fundamentally altered their fields, unifying and illuminating them in a way that no previous theory had done before.
So, what are these ideas? Oxford chemistry professor Peter Atkins outlined them in his 2003 book "Galileo's Finger: The Ten Great Ideas of Science". Atkins' breadth of scientific knowledge is truly impressive, but though the book was written with a popular audience in mind, it can be quite incomprehensible in places, even for people with a background in science.
The brains at Real Clear Science have parsed them all down to manageable form, though - so save yourself a month and read their 10 Greatest Ideas in the History of Science. Oh, and then go buy the book anyway, because you should.