'못','안' are used in the sentence to express negation. It is equivalent to the meaning of 'not...' in English. Since '못' and '안' both mean 'not', what is the difference? Think about it, both 'can't' and 'don't' have negative meanings, but if you think about it carefully, you will find that there is a difference in meaning between them. One means to negate at the level of ability, while the other means to negate regardless of ability.