Restarting fixes some problems because it removes temporary state. It does not repair hardware, improve a weak signal, or negotiate with a billing system. It just gives a confused process fewer things to remember.
That is why turning something off and on again is both a tired joke and a reasonable first step. Computers spend their day collecting small decisions: which network to use, what is in memory, whether a background task finished, which file is still open, and whether a connection from ten minutes ago deserves another chance. Usually those decisions are fine. Occasionally they pile up into a problem with no dramatic cause.
A restart clears the whiteboard
Programs use working memory as a whiteboard. They keep recently used data there because reading it again would be slower. They also keep temporary files, open connections, cached settings, and lists of things they intend to do later. This is useful right up until one of those things is wrong.
A program may be waiting for a reply that will never arrive. A service may have started in the wrong order. A browser tab may be holding an old version of a page while the page insists it has changed. A device may have connected to a network but failed at the less glamorous part where it actually gets useful traffic. None of this has to mean the device is ruined. It means the current session has become a bad meeting that no one knows how to end.
Restarting ends that session. Memory is cleared. Temporary connections close. Background tasks stop. On startup, the system rebuilds its short-term notes and asks the outside world what is true now. Sometimes that is all it needed.
Different restarts reset different things
Closing and reopening an application resets that application. Restarting a computer resets more of it, including services the application depends on. Restarting a router resets its connections and gives it another chance to talk to the provider. These are not interchangeable rituals, despite the impressive confidence with which they are often prescribed.
This also explains why a restart sometimes appears to work and then the problem returns. The restart removed the symptom, not the cause. A program with a memory leak can start fresh and slowly consume memory again. A flaky connection can reconnect successfully until it flakes out again. An update can temporarily behave after a reboot because it finally completed the installation it was waiting to do.
When to stop restarting
One restart is diagnosis. Five restarts is a hobby.
If the same problem keeps returning, notice what happens before it does. Does it fail after opening one file, joining one network, or leaving the device on overnight? Does another device have the same problem? Does an error message appear before everything gets vague? Those details point toward the cause far better than another ceremonial power cycle.
Restarting is valuable because it is cheap and reversible. It is not magic. It is housekeeping with a power button, which is less exciting but much more useful.