Always means without exception, every time, at all times. Read the verses below inserting those words: “without exception, every time, at all times be joyful”… Regardless of the circumstances, He is there and He is faithful and true.
See that no one repays evil for evil; on the contrary, always try to do good to each other, indeed, to everyone. Always be joyful. Pray regularly. In everything give thanks, for this is what God wants from you who are united with the Messiah Yeshua. ~~ 1 Thessalonians 5: 15-18