«اِلصَّاحِبِ اللِّي يْخَسَّرْ هُوَّا العَدُوِّ الْمُبِينْ»

The saying judges friendship by its results rather than by its label. Someone who calls himself your companion yet keeps bringing you loss has, through his actions, placed himself among your adversaries, and his harm is so evident that no claim of affection can disguise it.

The loss in question may be material, such as wasted money or failed dealings, or it may be wider damage to one's interests and wellbeing; the wording leaves this open. Either way, the point is that the cost of a relationship reveals its true nature, and a harmful friend deserves the caution owed to an open foe.

Fits moments of reckoning, when someone weighs a companion whose presence keeps costing them money, standing, or peace of mind. It can serve as a warning before trusting such a person further, or as a verdict after the damage is done.