So in our session last night, the party awoke from a nice Long Rest in a farmhouse en route to their latest task.  This was put in place by me to afford them a bit more background on the area and events they were chasing, with the added perk of a "safe" place to rest.  The intent was for them to wake up, eat and move on, leaving the little family behind as they continued on their adventure.  WELL.  Now they are planning to come back, on the way back through and give the Half-Orc a book they are creating, helping him learn to READ common and thus enabling him to teach the children there how to read and write Common and Orc.  Also some talk of training them in swordsmanship.  They have given the family 2 short swords, an axe and a shield.  Now I need to either create more for this little farmstead or find a way to remove it, lol.  

In another campaign where I am a player, my fellow party members and I were approached by "a guard" who told us of a problem at the city gates.  Well, my fellow party members needed a name, which the DM hesitated, looked around a bit, then blurted 'Terry"  Now Terry is a thing, with us having re-connected with him and getting him set up to train and maybe become something special.   The DM told us afterward, this "guard" was supposed to be a voice and nothing more.

So share YOUR tales of when a nothing in your campaign exploded into becoming something, due to your players grabbing it and not letting go.

I was DM'ing my party through Hoard of the Dragon Queen, which has an extended sequence where the party is traveling with a caravan and includes a bunch of NPCs with one-sentence descriptions... one of which is a Rock Gnome who just kind of sits on the last cart and wistfully watches the road behind them. I had misread the brief description and described him as a Deep Gnome, which instantly got some attention because they're so rare, and his sad, wistful nature instantly made everyone curious to investigate further. The book doesn't actually give any details about him, so it fell to me to come up with some reason why he was the way he was... so I came up with a story about him leaving the Underdark after protecting his Wife after she was infected by a Mindflayer, ignoring the incredibly obvious signs that she's no longer herself and ultimately getting his entire village killed, so he's constantly on the road because he feels like he's always being chased to be punished for what he did. The players spent a lot of time and resources getting to know him, helping him open up, and eventually helping him to connect with one of the dwarven guards who they also got attached to. His story was one of the big emotional beats of the campaign that helped one player open up a bit more, since she was mostly just playing a "greed for the sake of greed" trickster, mostly playing it for laughs and also just kind of focusing on a low-stakes personality so she could relax and enjoy the game more as an observer (our same group runs another game where she plays a much more tragic and involved character, and I think her trickster is kind of a way to take a break from that).

I was playing through the Lost mine of Phandelver as an intro to our campaign, and part way through it you get to a bosses base and there is a goblin called Droop who is a slave to bugbears. The Droop character is only really supposed to point the characters in the right direction and be free'd (or killed, as they tend to do with anything that moves). Well the party killed the bugbears, then armed Droop and gave him some armour, and he joined the party as an NPC. I was trying to get rid of him by making him recklessly run into fights and hopefully kill him off, but that spurred on the players to teach Droop how to be a better fighter, and not just befriending him but making him a full blown party member. Once they defeated the wave echo cave, they had a flameskull locked in a room and he was left there to guard the cave and prevent anyone from ever opening the room and releasing the flameskull.

Several months later, and a few level ups, one of the players gets killed by the green dragon, who has been tracking them to get revenge for looting and burning his lair from earlier in the story. The player decides to roll up Droop as a full blown character and is now playing as him as a level 7 ranger! He tracked the dragon to get revenge for burning down Phandelver and bumped into the party when they were in a pinch in the fight against the dragon.

I’m running a homebrew campaign and at one point my players are traveling through the territory of a young green dragon. In exchange for her not killing them (level 3) they promise to eliminate her rival, a green dragon wyrmling, who also happens to be her sister. But when they reach her cave, and I place her mini on the board, the players immediately exclaim: ‘Aw, she’s so cute! We’re not killing her!’

 Now the party is accompanied by Cee Cee, the accident prone baby dragon.

I had printed of a randomly generated city map and information for speeds sake.  When one of the players asked a townsperson if there was anything interesting about the town, I looked at the sheet and there it was:  A large chunk of obsidian sits in the center of town.  The townsfolk rumor that a demon is trapped at the center of it."

That was it.  They went on for 5 sessions tracking down the name of the demon, finding an alchemical means of obliterating the stone to get to the center and then summoning and defeating the demon.  Was NEVER in my plan but they had a blast tracking down the info on this demon.  

To go further, they had the town erect a sign (which they paid for) commemorating their deed.  Each time they did something cool they would have the town add more to the plaque.

This thread is great. 

I was making backgrounds for my party ahead of our first session of WBW.  I had one character who wanted to start as a Witchlight Hand, so I seeded relationships with other NPCs.  I wrote Nikolas in his ally box of his character sheet and put Thac0 in the enemies box, by which I meant more of a rival.  A Newman, for you Seinfeld fans.  Well, as they were investigating the missing stuff from the carnival, they kept convincing themselves that Thac0 was behind it all.  I leaned into it and made him the perfect jerk villain about it all.  But as the longest serving witchlight hand, he has all the info they're looking for, which he shared as a way of rubbing in their face how much he knew that they didn't.  They still knocked him out and ended up taking him to Prismeer with them after getting access to the crossing.  I have no idea why.  But now I have to come up with a whole character arc for this grumpy old clown while he's in the Feywild.

This isn't really appropriate, but I just wanted to mention that I also had an NPC named Thaco in my game... although in my case it was the name of my Goblin Bard's pet goat, and none of my friends got the reference.