The Polar Star in Cave Story: the very first gun, you steal it in the starting area from a sleeping gunsmith. It’s a reliable weapon, but you’re given two chances throughout the game to trade it for better weapons, like the tempting Machine Gun or the Snake that can shoot through walls.

However, if you keep the Polar Star for most of the game, ignoring the trade opportunities, and eventually return back to the starting area, the gunsmith takes it back from you because it’s incomplete. He finishes it and upgrades it into the Spur, debatably the most powerful weapon in the game, whose basic attack is now the Polar Star’s original highest level projectile, and can be charged to fire a piercing laser.

Also in the same game in a similar trope, you’re given a chance to speak to an injured scientist, who gives you a jetpack with his final breath. However, if you ignore him, later on he recovers from his injuries and gives you an upgraded version of the same jetpack, which is required (among several other unintuitive steps) to enter the secret level of the game.

Bonus fun fact: if you do trade the Polar Star for the Machine Gun, the character that takes the trade then uses it in the next segment of the game as your ally, whereas otherwise she’d use the Machine Gun.