It sounds like lazy tech support because the sentence is simple. The mechanism is not. A restart often works because complicated systems accumulate temporary state, and sometimes that state becomes nonsense.
CORE IDEAA reboot is not magic. It is a controlled demolition of temporary state followed by a return to a known starting condition.
Most failures are not this tidy, but the useful mental model is: running systems accumulate state; restarts discard a lot of it.
STATE
Your device is carrying around more temporary information than you can see.
Phones, routers, computers, televisions, cars, apps, and smart appliances maintain memory buffers, network sessions, cached data, background processes, device drivers, queues, timers, and connection tables. Most of that invisible bookkeeping is useful. Some of it eventually becomes stale, contradictory, or stuck.
A program can wait forever for a response that will never arrive. A network connection can remain half-open. A driver can hold a resource another process needs. Memory can leak away a little at a time. None of these require the entire machine to be physically broken.
RESTART
Power cycling removes assumptions.
When a device restarts, many temporary processes stop, volatile memory is cleared or rebuilt, hardware is reinitialized, services start in a defined order, and network connections are negotiated again. The system gets another chance to build its internal world from known inputs instead of continuing from a confused intermediate state.
That is why the ancient ritual works so often: it attacks an entire class of temporary-state failures at once.
NOT A CURE
If the same fault keeps returning, stop worshipping the reboot button.
A restart cannot repair a dying battery, damaged cable, overheating component, corrupted storage, defective sensor, bad configuration, malware, broken update, overloaded network, or failing power supply. It can temporarily hide some of those problems by resetting their symptoms.
If you restart the same thing every day, the restart has become evidence. Record what fails, when it fails, what else was happening, and how long the restart buys you.
ORDER MATTERS
Restart the smallest likely failure domain first.
If one app is frozen, restart the app before rebooting the whole computer. If one device has lost Wi-Fi, reconnect that device before rebooting the router. If every device has lost connectivity, then the router or upstream service becomes a better suspect.
This is fault isolation: change as little as possible while learning as much as possible.
BOTTOM LINE
“Turn it off and back on again” is crude systems engineering.
It works because complex machines can be healthy in hardware and still become trapped in unhealthy temporary states. Restarting throws away much of that state and rebuilds the system from a cleaner baseline.
If a reset solves the problem once, useful. If it solves the same problem every day, you have not solved the problem.
SOURCE TRAIL
Further reading.
FCC Consumer Guide — Home Network Tips includes router rebooting as a basic troubleshooting step and distinguishes home Wi-Fi conditions from upstream internet-service problems.