zuì jiǎndān de biānjiè shì rén hěn kuài huílái kěyǐ hěn jiǔ bù lái jiù bié zhàn

最简单的边界是：人很快回来，可以；很久不来，就别占。

The simplest rule is: if someone comes back soon, it's okay; if not for a long time, don't occupy it.