system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do phones have so much trouble when switching from WiFi to data?

I notice this all the time, typically when I'm leaving my house and trying to do something that requires an internet connection. Our smartphones seems incapable of smoothly transitioning from WiFi to data and seem to need to have everything closed and re-launched to figure itself out.
gpt
A lot of phones are designed to tap in to one network or the other. Once you connect to the Wi-Fi network, it disconnects from the mobile network. When you disconnect from the Wi-Fi, it has to reconnect to the mobile network, authenticate itself and pass some data back and forth before you can start using it.