They say that when you meet your mate you know it straight away. It just takes one look, and you’re done.
When Derek looks at Stiles - tiny, fragile human who insists on running with the wolves - the only thing he feels is rage.
Derek wants to grab him by the shoulders and shake him, yell that he has no business being pack, that if he stays he’s going to trip and fall and no one will be there to save him because Derek can barely save himself, let alone other people. Other humans, who never showed compassion or understanding. Who always ostracized him, making him feel unwanted and a stranger in his own land.
Sometimes Derek wants to listen to his wolf, wants to physically harm the kid - just to show him that when you run with the wolves you’re bound to get hurt, bound to end up in a coffin. Just like Laura. Just like his parents. Just like uncle Peter. Just like anyone he’s ever met.
Derek wants to tell Stiles he’s being an idiot, that he shouldn’t waste what he has. That he should stop endangering himself while he still has a father - that while Derek has nothing to lose, Stiles has a whole life in front of him, and that’s a gift he should cherish, not handle carelessly like he always does.
But Derek says nothing, and when Stiles keeps on running with the wolves, Derek finally knows.