Reasons

The world could be a cruel, wicked place, filled with nightmares and terrors unending. Erwin Smith made the choice to throw himself into those nightmares, but even the most steadfast man is not an island. At the very least, there was someone he could fall back on, even if it took him some time to realize it. (Erwin backstory-centric, the slowest of slow burns. Cross-posted on AO3)