Following St. Jerome's interpretation of St. Matthew's invocation of Isaiah's "smoldering wick" as signifying "a weak spark of faith in a little one," let me propose three categories of people with a weak spark of faith:
Those who know their faith is weak.
Those who have never thought about whether their faith is weak.
Those who are convinced their faith is strong.
I'm always nervous around people in the first category, for fear that anything I might say to strengthen their faith will wind up snuffing it out.
Those in the second category are at risk of having their faith snuffed out -- by sudden suffering, for example, or even just long-term tepidity -- before they even notice it was only ever smoldering.
Those in the third category are like a man who has built his house on rock, in an earthquake zone. The rain fell, the floods came, and the winds blew and buffeted the house, but it did not collapse. Then came the earthquake, and he was lost.