The Psalter that gets quoted at funerals is a small and well-behaved selection of the Psalter that exists. Twenty-three. Ninety-one. The green pastures and the shadow of the Almighty. All of it true, all of it load-bearing, and all of it about a third of the book.
The rest is louder.
The complaint is inspired too
Roughly a third of the psalms are laments, and they are not gentle. They accuse. They ask how long. They tell God to wake up. Psalm 88 ends without resolution — the last word in the Hebrew is darkness — and it is in the canon, unamended, with no editor appending a hopeful couplet.
Which means the complaint is not a failure of faith that God tolerated. It is speech God provided. Someone was handed these words to say.
What we do instead
When a person is in the worst week of their life, we tend to give them the calm psalms, because we want to give them comfort. The effect is subtler than we intend. It communicates that the acceptable register for talking to God is composed, and that whatever they are actually feeling should be resolved before it is brought.
So they bring the resolved version. Which is to say they bring less than the truth, which is to say they pray less honestly, which is exactly when people quietly stop praying.
A better handoff
Give them Psalm 13. Read it out loud, all six verses, including the turn at the end that they will not feel yet — and tell them that the turn took the psalmist an unknown length of time and that the text does not say how long.
The comfort in the lament psalms is not that they resolve. It is that someone else has already said this, in these words, and it was written down and kept.