There are several verses in the Bible which specifically talk of thankfulness.

eg Give thanks for everything  Ephesians 5 V20

Always be thankful  Colossians 3 V 15

Sing with thankful hearts  Colossians 3 V 16

Have a thankful heart  Colossians 4 v 2

Be thankful in all circumstances  1 Thessalonians 5 v 11

Be thankful for the unshakeable kingdom Hebrews 12 v 28

The Question is. Can the Christian really expect to be thankful in ever circumstance given the bad things that happen in this world?