“To be thankful” means to concentrate these positive moods and associate them with an image, with a representation. If you have previously linked positive states in this way, you can, upon finding yourself in a difficult situation, evoke that representation, and along with it will arise the positive quality that accompanied it earlier. Furthermore, since this mental “charge” has been increased through previous repetitions, it is capable of displacing the negative emotions that certain situations impose.
Whenever you find great strength, joy, and kindness in your heart, or when you feel free and without contradictions, immediately be internally thankful. When you find yourself in opposite circumstances, ask with faith, and the gratitude you have accumulated will return to you transformed and amplified in benefit.