I don't think this means to pray hardest when we're in the most trouble. Most of us find it pretty easy to pray when we need God to get us out of a tight spot. For me, this quote means that I need to pray hardest when I'm . . .
. . . exhausted
. . . excited
. . . angry
. . . anxious
. . . annoyed
. . . busy
. . . behind
. . . distracted.
When is it hardest for you to pray? Let's work harder at remembering at that moment to pray for God's strength, comfort, wisdom, and grace.