Holy Righteous John of Kronstadt teaches:
“When you begin to pray to the Queen Theotokos, before praying, be firmly confident that you will not leave Her without receiving mercy. To think this way and to be confident about Her is worthy and righteous. She is the all-merciful Mother of the all-merciful God the Word, and all centuries and all Christian churches proclaim Her mercies, innumerably great and countless. She is definitely an abyss of goodness and generosity, as it is said about Her in the canon of Hodegetria (canto 5:1).
Therefore, to approach Her in prayer without such confidence would be unreasonable and impudent, and doubt would offend Her goodness, just as the goodness of God is insulted when one approaches God in prayer and does not hope to receive from Him what is asked.
How do they rush for mercy to some high and rich person, whose mercy everyone knows, who has proven his mercy through numerous experiments? Usually with the calmest confidence and hope of getting from him what they want.
So we must not doubt in prayer, and not be cowardly.”