My friend or business partner deceived me, and now I cannot decide whether to keep giving them chances or protect myself. Where is the line between mercy and being naive?
Being deceived by someone you trusted leaves two wounds, the loss itself and the loss of confidence in your own reading of people. The second one takes longer to heal. It is not a fault in you that you trusted; trusting was reasonable with what you knew then, and now you know something you did not know before.
Our religion has never asked anyone to be soft toward their own harm. The Prophet, peace be upon him, said something short enough for a merchant or a mother to live by.
“A believer is not stung twice from the same hole.”
The Prophet (peace be upon him), Sahih al-Bukhari & Sahih Muslim (Bukhari 6133 / Muslim 2998) · meaning
Notice what this permits. You may keep your heart clean of hatred while your hand grows wiser about which doors you open again. Caution about a person’s dealings is not suspicion of their soul.
Forgiveness is given a high rank too, though not the kind that pretends nothing happened.
“And whoever is patient and forgives, indeed that is of the matters requiring firm resolve.”
Qur’an, Ash-Shura 42:43 · meaning
Forgiveness here is called resolve, not weakness. You can let go of the resentment, which frees you more than it frees them, and still decide calmly that you will not hand them your affairs a second time. One is a gift to your own soul. The other is ordinary prudence.
There is a third guard, and it points the other way. The pain of what was done to you must not tip you into being unfair to them in return.
“And let not the hatred of a people prevent you from being just. Be just, that is nearer to piety.”
Qur’an, Al-Ma’idah 5:8 · meaning
Those who study how broken trust is repaired arrive at the same balance, forgive the person, watch the pattern. Mercy in the chest and open eyes in your dealings are not opponents; they work together. That is where the line falls.
One small step: Today, release this person from your resentment and make one short dua for their guidance. Then settle one clear safeguard for any future dealing, a written agreement for instance, and let trust return in small, verifiable steps rather than all at once.