When you boil it down, "The Truth" in JW-land is a subliminal message that is and has been stressed that the JW's have in long, confusing talks. It is a form of a code word. It means everything to the JW but nothing really to outsiders. They use it as an anchor-word where if you ever try to leave you won't be "in" the truth (JW definition) and you will be missing out on hearing the truth (dictionary definition) about this world. It's a word that inspires fear - they are implying they have the only truth (dictionary definition) or the real meaning behind everything that is happening and everything outside their definition of truth is inherently false.
If a scientist proves that people have been around longer than 6000 years, he does not have the truth or he is not in the truth and thus he is false. If a doctor tries to give your kid a blood transfusion, he does not know the truth about it and he cannot understand it since he is not in the truth.