system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does my iPhone struggle to load a 2 min youtube video, but streams Netflix seamlessly?
gpt
There are differences between Netflix and Google/YouTube.  One is a paid subscription one is a free ad sponsored site.  The subscription based Netflix has all the episodes spooled up and ready to go on each server - they know exactly what to anticipate prior to release.  That being said, even their House of Cards and Orange is the new Black etc. on release day are subject to massive peak usage and that's hard to scale.  YouTube appears to propagate videos differently.  Every time you watch a relatively obscure video, or something that hits the 301+ mark can bring traffic congestion/slow speed serving up an unexpected video.  

To cut some people off at the pass, the reason ads are so flawlessly delivered is because 1) Money.  Ads aren't free, someone pays directly for them, Google has a vested interest in serving them up quick.  2)  there's thousands pre-uploaded ads vs. tens of millions of random user generated videos.  Ad servers can be curated much more easily than a user generated dumping ground.