a) Write bad code (you barely know the syntax)
b) Get really confused, and thus either start hating it, or simply not able to take full advantage of the framework.
c) Do roundabout ways to solve a problem when there is a very simple solution, but you not understanding the language still made the mistake.
d) Hit a big brick wall when looking at code others made.
I made this sort of mistake before. It is a bad mistake to make.
However to note: jQuery makes dom manipulation fairly easy. It is in no way a replacement to javascript, only the browser's dom lib calls. You just wind up not writing a bunch of utility functions to handle the different ways to get at the same information in the browser. Plus I like the syntax.