I went into the woods and got it.
I sat down to seek it.
I brought it home with me because I couldn't find it.
What is it?
I thought of "tick" and I think it's the best answer. "Splinter" doesn't fit--you can certainly find a splinter, even though you can't remove it easily. And, peace, serenity, etc., don't make sense, because you wouldn't seek it after you got it.
But a tick you might see crawl up your sleeve or pant leg, and then you can't find it. Along the same vein, in more tropical woods, "leach" might fit.