“I have strayed like a lost sheep.
Search for your servant,
For I have not forgotten your commandments.”
~Psalm 119:176

Who wrote Psalm 119?
Though the writer’s name is unknown, we can form a portrait of where he (or she) was in life by some of his expressions.
Although verse one affirms: “Happy are those who are blameless in their way […]” the psalmist is not applying these words to himself, for verses five and six explain: “If only I could remain steadfast so as to observe your regulations! Then I would not be put to shame when I consider all your commandments.”
The psalmist is evidently undergoing some type of affliction as a consequence of past mistakes.
Even though he no longer ‘goes astray,’ he is still an object of “scorn and contempt,” targeted by insensitive, presumptuous liars (Ps. 119:22,67,69,70).
Although the psalmist does suffer sleeplessness and grief, this allows him to find comfort in his knowledge of Jehovah God (Ps. 119:28,52,55).
The psalmist goes so far as to say that his spiritual heritage is the ‘joy of his heart,’ (Ps. 119:111).
What fueled his strength?
Verses 92-95 read:

If I had not been fond of your law,
I would have perished in my affliction. […]
I belong to you; save me […]. The wicked wait to destroy me,
But I give close attention to your reminders.”

Time and again, the psalmist references his bond with God and love for God’s Word as the reasons he can bear his affliction and carry on.
Undefeated, he resolves to fulfill his vows to God and rely on His justice and loyal love (Ps. 119:106,149).