It is extremely unlikley that Jesus, talking to Saul from heaven in the Hebrew language [Act 26:14], would have actually said the Greek words that translate to "It is hard for you to kick against the goads".
Luke does not record these words in the Acts 9 (although they are added here in the Textus Receptus [KJV]) or in the Acts 22 account. In these two accounts it is more likely that Luke is recording the testimony of someone else, other than Paul, telling him about these events. Although we know that is is very likely that Luke was there to hear the testimony of Paul in Acts 26. Perhaps he even had access to the written court records.
I believe the best explanation is that what Jesus did say to Saul on that day was a Hebrew idiomatic expression, not the Greek one that Luke records in the Acts 26 account of Paul's testimony.
So what did Jesus actually say? That is, if He said any idiomatic expression at all; perhaps this is an embellishment that Paul made in his testimony or that Luke added for clarification or perhaps the "court reporter" added it as a translation of the actual Hebrew words that Paul actually did say in his testimony.
Of course we can never know, but what most likely happened is that Jesus did say Hebrew words that make up a Hebrew idiomatic expression that means the same thing as the Greek words that make up the equivalent Greek idiomatic expression.
The literal translation of an idiomatic expressions is sometimes very unclear to the true meaning. The meaning of what Jesus actually said (if He did actually use a Hebrew idiom) is, "your attempt to resist is futile".
Perhaps the Hebrew idiom (lost to history because it is nowhere recorded) was something like, "Saul, why are you spitting into the wind?" Perhaps in Luke's notes for what became Acts 9 & 22 he had written this Hebrew idiom, but not wanting to confuse people with a literal translation of an idiom, he decided to just leave it out.
However, when Paul, or the court stenographer, or Luke himself recognized that the meaning of what Jesus actually did say was appropriately conveyed by the well know Greek idiomatic expression "It is hard for you to kick against the goads", that is how we ended up with those Greek words in our Bibles.
I can picture Luke saying to Paul after the proceedings, "So that is what "enchsh amnshk aui lik" means!" Perhaps he even crossed out the Hebrew idiom in his notes for what became chapter 9 and added the Greek idiom with an arrow in the border, and that is why it got added to the Textus Receptus!
Blessings, I hope this is helpful. SalasinSalvation