三心二意
Meaning
Half-hearted and indecisive — starting many things without committing to one.
In a sentence
Learning an instrument is hard if you are 三心二意.
Usage note
Criticises inconsistent effort rather than lack of ability.
Where you see it in Brain Challenge
This idiom appears in the picture-idiom levels as a picture or number clue. When the clue shows numbers, the digits usually become the first characters of each half of the idiom — that is why so many chengyu start with 一, 三, 五, 七, 九 or 十.