[ArathornJax]

In speaking of both Faramir and Boromir, this quote by Gandalf at Minis Tirith to Pippin about the Lord Denethor I have found interesting:

"He is not as other men of this time, Pippin, and whatever be his descent from father to son, by some chance the blood of Westernesse runs nearly true in him; as it does in his other son, Faramir, and yet did not in Boromir, whom he loved best."

If Denethor's heritage is from Westernesse (mixed with other houses since coming to Middle Earth) and in him the blood of Westernesse runs true, and it also runs true in Faramir, then what did Tolkien mean that it did not do so in Boromir? Does this account for some of the differences between Faramir and Boromir? How did Faramir's blood run true but how did Boromir not run true? Thoughts would be appreciated as I am thinking on this since I read it last night.