In the garbage is a little bit of an overstatement. I mean, I
remember the stuff. But it's hard to reuse because it's fairly specialized. Either because the stuff was focused on the PCs, or because the campaign's specific circumstance are hard to repeat. Let me show you my DMing history.
Game 1: Standard adventuring group wandering FR-like homebrew. Internet group. Lasted 1 1/2 years. Campaign lost steam. Played with group but not as DM.
Game 2: Superheroes in Champions campaign setting. Internet group. Lasted 6-8 months. DM buckled under weight of HERO system, ability to contend with one PC. Played with same group but not as DM.
Game 3: Detectives running an agency in Sharn. Game lasted 3 months. Internet group, players couldn't stay reliable/dedicated. Never played with the group again.
Game 4: Motley crew of Sharn PCs. Internet group. First adventure: module that forced PCs to work together. Afterwards the game fell apart as PCs motivations and personalities conflicted. Never played with group again.
Game 5: Group going into demon-infested desert to clean out a community on the edge of the water. Eberron game, internet group. Lasted a month. Player/DM interest waned. Never played with the same group again.
Game 6: Colony game. Face to face group. Game lasted 6-8 months, then DM stick was offered to pass around. Gaming group fragmented soon after. Never played with same group again.
Game 7: Wandering gypsy con artists. Face to face. Game lasted 4 months. Designed to be a short campaign from the onset. Never played with group again.
Game 8: KotS. Internet group. Lasted about 3-4 months. DM had to bow out of group due to RL complications; DM stick was handed off. Played with 2 PCs from this group again.
Game 9: Casual game with 2 players wandering around. Internet. Lasted 3 sessions. Waning interest and RL complications. 2 players from game #5.
Game 10: Group seeking to save the world. Homebrew setting. Lasted a few months. Internet. RL complications and other flaws caused end of game. 2 players from game 7.
Game 11: Colony game. Face to face group. Game lasted 1 session. Group and DM had different tastes/assumptions in gaming. Never played with group again.
Game 12: Colony game. Yet to start. Same group from game 9.
Now, I
have used the same adventure (tailored slightly) for groups 1 and 3. I'm obviously trying to use the same campaign for groups 6, 11 and 12. I could
try to use a few things from games 1 and 9, but aside from that, what went on just does not "track". Everything else has either existed in a different world, or the setting just doesn't work with it.
Also it varies so much because I'll ask "What game do YOU want to play in?" and build the campaign around their answers and preferred style (games 3*, 7 and 8*). Or I've created several ideas and presented them to the group, asking which appeals to them the most (game 6 and 8) . Although with the last two groups I've decided I want to run That campaign.
*Amusingly enough, I was actually recruited or volunteered to run these games after player(s) decided they wanted to play that ahead of time.