Probably the latter. It's human nature.
Can we change that? Can we learn to be thankful even when things don't always go the way we'd like? Do we have the grace to stop complaining and questioning God's motives -- the courage to accept what He deems right for us?
The Bible commands, "Give thanks in all circumstances, for this is God's will for you in Christ Jesus" (1 Thessalonians 5:18, NIV).
Even in the midst of trials we can thank God, because we know that He has promised to be with us and that He will help us. We know that He can use times of suffering to draw us closer to Himself: "Consider it pure joy, my brothers, whenever you face trials of many kinds, because you know that the testing of your faith develops perseverance" (James 1:2-3, NIV).
When the prophet, Daniel, learned that evil men were plotting against him to destroy him, "he got down on his knees and prayed, giving thanks to his God, just as he had done before" (Daniel 6:10, NIV).
I don't know what difficulties you may be facing right now, but God does; He loves you and is with you by His Holy Spirit. That's why it's important to develop a spirit of thankfulness even in the midst of trouble and heartache.
We learn so much more in times of sorrow than in times of joy. Consider these words by Robert Browning Hamilton: "I walked a mile with pleasure, she chattered all the way, but left me none the wiser for all she had to say. I walked a mile with sorrow, and not a word said she ... but oh, the things I learned from sorrow, when sorrow walked with me."
If affliction causes us to learn, then we must be grateful to God for it.
When we suffer, yet keep praising God, it gives Him glory. And if God is being glorified in our life, can we not thank Him, even though we may not feel thankful at the time?
Real faith is not receiving what we want from God. It is graciously accepting what He gives us.