In every thing give thanks: for this is the will of God in Christ Jesus concerning you.
εν παντι ευχαριστειτε τουτο γαρ θελημα θεου εν χριστω ιησου εις υμας
1 Thessalonians 5:18
The same idea in other traditions
Then do ye remember Me; I will remember you. Be grateful to Me, and reject not Faith.
Enter into His gates with thanksgiving, and into His courts with praise; give thanks unto Him, and bless His name.
Why forget Him, who has given us everything? Why forget Him, who is the Life of the living beings? Why forget Him, who preserves us in the fire of the womb?
The true person is grateful and thankful, for the virtuous only know how to be grateful and thankful. It is totally the level of a true person to be grateful and thankful.