Smartphone functions properly when restarted

[neku]

For almost one day, I could not use any app on my smartphone, the app was closing automatically. When I restarted it, it functioned properly. What could be the reason why the smartphone was malfunctioning?

 

[eLdavis]

It might be a simple malfunction since it has been working for long, so a simple restart made it better, or maybe it's due for formatting.