If something harmful or undesirable is left unchecked, nobody controls it or prevents it from growing or developing.
双语例句
例： If left unchecked, weeds will flourish.
如果不加遏制，杂草就会疯长。
例： a world in which brutality and lawlessness are allowed to go unchecked.
一个野蛮与无法无天横行无阻的世界。