Why is Netflix showing me content in low quality?

Check your internet connection first, because Netflix automatically lowers the quality if you don't have a stable speed; then check in the app settings that you haven't intentionally limited the playback quality.

What device are you using to watch, and how long has it been since you last restarted the app?

The thing people often forget is that Netflix stores a pretty aggressive local cache. If the app's been running for days without being fully closed, it builds up junk and starts messing with streaming. Try actually closing the application (not just minimizing it) and opening it again. On smartphones sometimes you also need to go to settings > apps > Netflix > storage > clear cache. You won't lose anything, it's just temporary stuff the app will redownload.

The other thing is that Netflix has weird algorithms for estimating your connection. If you had a speed dip a few days ago, the app might've decided you're in "weak connection mode" and keeps giving you low quality even though your connection's back to normal now. The trick is to force a refresh: go into your Netflix account settings from a browser (not the app), hit the "Recent viewing activity" section, and sign out all devices. Then sign back in. It forces Netflix to reassess from scratch, and usually it'll kick off with higher quality if your line can handle it.