Let's look at ways this quote is true:
Many people believe that in order to have happiness we have to have looks, money, nicer cars, bigger homes, more "stuff". If we believe this same way, are we believing something that is true? Nope. True happiness can't be bought. Things might make us happy for a while, but not for long.
Here's another one: Suppose I think I am worthless, that I can never do anything right, or that I have to be perfect in order for someone to love me. Is it true? No. Again, not true. No one is worthless. Each one of us is worthy. We're all "somebody" to someone. We are very special to God because He made us. He loves us. I don't have to be perfect - in fact I can't be perfect on my own, but when God looks at a Christian through the blood of Jesus, He sees a perfectly saved child.
Now let's look at it another way. Maybe I believe that ,"I'm basically a good person. I try to help others. I'm a law-abiding citizen. I'm honest. I love my family. But Christianity? I don't have time for that. I don't like that religious talk. God will never punish a "good" person or condemn such a person to hell. I at least know that He's known to be loving. What kind of loving God would do that?" Are these statements true? Some of them. This person may very well be "good" in all of those ways, but does God save anyone because of their goodness? No. He doesn't. I can never be good enough to be saved. I can never be good enough to go to Heaven. God prepared the way of salvation and the only way is through His Son, Jesus Christ. It's because of what He has done, not because of what we have done.
So, what do you believe? What do you think? Can you believe everything you think? Maybe yes. Maybe no. How can we know? By searching for the truth in everything. The truth is found in God's Word...the Bible. Each of the scenarios I gave in this post....all of the untruths.....all of them in the "true" form can be found in the Word. Every one of them! The Bible is the only source of what is true and right.
Only believe what you think if what you think is truth.
Finally, brothers and sisters, whatever is true.....think about such things.
To the Jews who had believed him, Jesus said, “If you hold to my teaching, you are really my disciples. Then you will know the truth, and the truth will set you free.”
Jesus answered, “I am the way and the truth and the life. No one comes to the Father except through me.