How/Where do people find so many fitting movie/meme clips for short edits?

Ive noticed that a lot of the videos i watch on youtube have sound or video inserts from memes or movies that fit well with the jokes going on in the video. What im wondering is, how do the editors find these? I know you could probably just remember some fitting ones, but even as someone who has been enveloped in internet culture for all his life, i have a hard time actually remembering fitting meme clips or movie clips.

Is there some kind of repository online, or is it just something that good editors personally build up over time?