Did Law Really Say “Don't Try to Find a Reason for Somebody's Love”?

No. Trafalgar Law is the man the line is said to, not the man who says it. "Don't try to find a reason for somebody's love" is Sengoku's, spoken to Law at the end of the Dressrosa arc, and it is one of the better-sourced lines in the One Piece corpus: ComicBook.com prints the whole speech in a sentence and Game Rant prints the sentence on its own, and the two are separately owned newsrooms.

The verdict

Misattributed. ComicBook.com's ranking of the ten best One Piece quotes carries the full passage in its body text, credited to Sengoku and placed at episode 743: "Don't try to find a reason for somebody's love... If you really wanna do something in his memory, both you and I should always remember him. That's good enough. So live your life as you like. That's what he would say." Game Rant's feature on Law and Corazon prints the first sentence, also credited to Sengoku. Those are two publishers, not two mastheads of one, which is the standard this site asks of anything it calls double-checked. Wikiquote has nothing: its One Piece pages stop at East Blue, and a search of the whole site for the phrase returns zero. So the wording rests on the editorial tier, and the speaker rests on every source there is.

Whose line it is, and why it gets Law's name

Sengoku is the retired Fleet Admiral, and Donquixote Rosinante, the Corazon of the Donquixote family, was the Marine he raised and sent undercover into his own brother's crew. Rosinante died getting a sick child out of that crew, with a Devil Fruit that could cure him. The child was Law. Thirteen years later, in the quiet after Dressrosa, Law asks Sengoku the question he has organized his life around: was Corazon looking after him because of the D. in his name, because of something in his blood, because there was a plan. Sengoku's answer is that there was no plan. He loved the boy. Stop looking for the reason and live.

That is why the line travels under Law's name. It is his scene, his flashback and his face on every edit, and the question it answers is his. A video captioned as a Law quote is not lying about whose story this is, only about who is talking. The pattern is the one that filed Dr. Hiriluk's speech about being forgotten under Luffy: the camera is on the famous character, so the caption follows the face. None of the written Law quote lists we checked carry it, which says something. The people who type out Law's lines know it is not his. The people who cut thirty-second edits do not always.

Why the wording matters here

The sentence on the poster is the first of five. Stripped of the four behind it, it reads like advice about romance, and it is often shared that way. The rest of the speech is about a dead man and what to do with his memory: remember him, the two of us, and that is enough. Sengoku is talking as a father about a son, to the son that son died for. Give it to Law and the grief moves to the wrong side of the conversation. Law is not the one consoling; he is the one being told to put the question down.

What to quote

ComicBook.com's full rendering, with Sengoku's name on it, and the episode. The short version is fine as a caption as long as the name is right. Law does not have a page on this site yet: his own best lines, about the weak not choosing how they die and about the Straw Hats making miracles, have no primary source and no body-text editorial rendering that we have found, and the One Piece hub carries only what can be sourced to that standard. Sengoku has no page either. Both would be welcome once the sourcing exists.

How we checked

The verification process asks for a primary or editorial source printing the line inside a sentence rather than as a title-cased heading. Two independent editorial sources do that here and both name Sengoku; nothing that names Law as the speaker gives a scene, because in no scene does he say it. The entry in the fact-check database is misattributed. If a reader finds Law saying it anywhere, the contact page is open and the verdict will change.