Given that we must be cautious about relying on our own thoughts whether they are good or bad, certain good thoughts are still useful for our spiritual growth.
Elder Paisios says,
We should keep in mind that God "cannot" help us, even if He really wants to, unless we acquire a positive way of thinking.What kind of positive thinking is he talking about?
He offers the example of the two thieves who were crucified with Jesus. They both died, but one was granted a place in heaven with Christ. The thief on the left thought negatively saying, "Are you not the Christ? Save yourself and us.' (Luke 23:39) The one on the right thought differently. He rebuked the thief on the left saying, "Do you not fear God, since you are under the same sentence of condemnation? And we indeed justly; for we are receiving the due reward of our deeds; but this man has done nothing wrong." This man then turned to Jesus and said "Jesus remember me when you come into your kingdom." (Lk 23:4--42) Jesus then said to the one on the right, "Truly, I say to you, today you will be with me in Paradise." (Lk 23:43) Both of these men stood next to God on the Cross. One on the left received no help from Jesus, but the one on the right even though he knew his guilt of terrible crimes moved Jesus with his positive thinking.
The kind of positive thinking he is pointing out that is essential is being positive about our relationship with God; Not good thoughts about our own egotistical earthly needs. No matter how badly we have failed in living the commandments, when we are repentive God can help us. This is an example of the positive thought that is essential for our salvation.
Source: Elder Paisios from the Holy Mountain, p 31