In the world that we live in, tainted by sin, Satan desires for God's creation to turn away from God and deny Him. Satan plants these lies in humans' heads, making the person think they are true. This is what it means to walk around thinking "my truth" is the "truth."
But there comes a problem with this. How can so many different people have versions of "their truth" for it to even be regarded as the "truth?" After all, the sole definition of the word "truth" is "that which is true or in accordance with fact or reality" (Oxford Languages). If there are contradicting truths among people, then how can one even call it a "truth" if it is not in accordance with fact or reality?
The answer lies in that people wander away and deny the actual Truth, the Truth that is from God revealed to us in the Bible. Scripture tells us that Jesus is "The Way, the Truth, and The Life" (John 14:6). Scripture also tells us, "The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the one and only Son, who came from the Father, full of grace and truth" (John 1:14). God, in His perfect character, cannot be dishonest, as that would corrupt His character. Truth is a core part of God's character, revealing His truth through Scripture by inspiration of the Holy Spirit.
Scripture states in 2 Timothy 2:15, "Do your best to present yourself to God as one approved, a worker who does not need to be ashamed and who correctly handles the word of truth." The word of truth comes from God that was revealed to His people, meaning the Truth (plain sense of what is correct) is from God. John 1:17 goes further into explaining how the very sense of Truth comes from God: "For the law was given through Moses; grace and truth came through Jesus Christ." 2 Timothy 3:16 talks about the truth of God's Word in Scripture in its infallibility: "All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness." John 17:17 puts it plainly: "Sanctify them in the truth; your word is truth."
So then, what can we do knowing God's Word is the Truth? Scripture gives us hope, stating "Then you will know the truth, and the truth will set you free" (John 8:32). God made the promise in Jeremiah 31:33, promising that He would write His Law on our hearts. This Truth was carried through by the promise of the Holy Spirit to those who believe. John 16:13 goes into this more, saying "But when he, the Spirit of truth, comes, he will guide you into all the truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come." The Holy Spirit within us bears witness to the actual Truth, guiding us in how we should conduct our lives to align with God's truth and for His glory.
The difference between man's "truth" and God's Truth revealed through Scripture, is that man has a false, deceptive sense of truth, inspired by the "father of lies" and the "one who has no truth" who is Satan (John 8:44). God's Truth, on the other hand, is the actual Truth, revealed through Scripture that is good and righteous.