When I started cooking a decade ago, I followed recipes to the ounce. It wasn't my style though, even back then. It is not that I like to break the rules, but I definitely bend the rules a lot - ask my friends and family. I want to know where the line is and then I want to walk on it as if it was a tightrope.
Through my years of recipe testing, and many many failed dinners (just ask Jim), I learned the hard way what works and what doesn't. These trial and errors have given me the confidence to make substitutions in recipes when I find that I left something off the grocery list. If you are new to cooking, extend yourself some grace.
For those that are timid to try a recipe that seems complicated, ask yourself what is the worst thing that could happen. Dinner could taste awful, and you order pizza. But I bet you will have learned something through the experience. Don't be scared.