Let's take a look at what is expected of the first line.
Narrator's voice, character, setting and the most anticipated, some sort of conflict. Some of these things can't fit into every first sentence. There are times where you need to pick and choose what would grab the reader most, and follow up the rest of the needed elements in the rest of the first paragraph. Making not just the first sentence the hook, but the first paragraph.
Examples of first sentences.
Delta Pi by Andrew Bert:
Kinsey Stafford noticed it—or, rather, the effect of it—in his office at the Center for Mathematical Studies,
Andrew Bert shows in his first sentence the character: Kinsey Stafford. We can picture where Kinsey is, just by knowing he's in an office. It also shows voice in the way that Andrew Bert words his first sentence.We do not see conflict yet, but it gives the the presence of the main character.
His chest tightened and he hung his head in grief. His program to calculate the deep digits of pi had suddenly crashed. In a race against time to save his career, he'd just lost precious months' work
With the rest of the paragraph not only do we find the conflict, but the provoking conflict that will drive the entire story.
The Watchtower by Darke Conteur:
Napoleon Bonaparte once said that there were two motivation to move men; inspiration and fear, but for Martin Cunningham, starvation was a damn good means of motivation too.
Darke shows in this one sentence a powerful drive of voice, character, and conflict. A good mix to keep the reader going.
I challenge you to pick up your favorite book. Does it have a good opening line, one filled with character, voice, setting and conflict? If not, does the rest of the paragraph lend a hand in this. Perhaps the rest of the chapter? Sift through your library and check book after book. Sometimes it only takes one line to grab you till the end pages.