I hate writing the first sentence more than any other sentence (even more than the last one). You simultaneously want to say everything all at once, but cannot find an origin that makes sense on its own and smoothly transitions into your future thoughts. (I do admit that the title and first sentence of this particular post happen to work nicely.)
There are two kinds of writers: Those who suck at starting things and those who suck at finishing things (there is a third type: those who suck at everything, but they tend not to actually do any writing.)
I happen to be the former. And if you, also, can never manage to come up with a good beginning, then skip it. Jump straight into the body. Get done the parts you can do. Write down all the things you want to say. Then figure out how to put them together after you get it all done.
One of two things will happen: Either you will discover a good intro as you write the bulk of your piece, or you will logically deduce the best possible intro during the time that you are piecing together all the other parts.
Writing is the opposite of meal time. Do not save the best for last. Voraciously consume as many pages as possible as fast as possible. If you're lucky, you will slog through the nasty parts just out of habit or an obsessive compulsion to complete what you've started.