When Lyra Silvertongue first used the alethiometer, she thought knowing the truth was a neat thing, for a young girl.
She'd know what would happen ahead of time. She'd know things that the adults did not. She could do so much, after all, with the truth.
Yet she soon found out that knowing the truth isn't at as neat as she thought it would be.
When she tried to use it too find out if Will Parry, the boy she loved, would go back to his own world, and she to hers, she was happy that the alethiometer wasn't working anymore. That maybe, the simple revelation was just a lie. That maybe, it wasn't the truth and they could live happily ever after.
But she knew better.
She decided, soon after, that knowing the truth isn't as neat as it was once.
Because some things are better left a lie.