You know that He is the source of all good - indeed, that He is goodness itself. You know that as the Creator of all that is good, He is infinitely more to be desired than the most desirable of His creatures. He is better than any earthly pleasure, any this-worldly happiness, any present success. You know, as St. Augustine discovered, that "You [God] have made us for Yourself, and our heart is restless until it rests in You."
You know all that, and yet sometimes, it doesn't feel like the knowledge is enough to convince the will to say "no" to the present temptation.
Why? Why are we silly enough to refuse to listen to God in order to have our way on things that'll all pass away so swiftly?
Original sin. As Fr. Michael Gaitley, MIC, explains in The 'One Thing' is Three, original sin had some fairly dramatic consequences:
humans now have darkened intellects - it's harder to know the truth (for instance, that you're eating unhealthily and need to stop);
humans have weakened wills - it's harder to will the good (like choosing the salad);
humans have disordered desires - it's harder to want the good, and easy to want the wrong thing at the wrong time in the wrong way (like several tubs of ice cream instead of that salad).
These are three burdens that have been passed down from our first parents to all generations, all of humanity - except for a few.
Our Lady is the Immaculate Conception, preserved free from all stain of original sin. Her intellect, will, and desires are not only healthy, strong, and rightly ordered, but they're all raised by grace to perfection beyond our imagining.
So when we commemorate the Presentation of the Blessed Virgin Mary on Nov. 21, we're celebrating the dedication of God's greatest creation to her Creator. She's the greatest gift humanity has received, short of her Son, and she's the greatest creature, by the grace of God, consecrated to God's service. You and I may have times where we fail to faithfully respond to God's gracious gifts - she never said no, never preferred a creature over her Creator, never resisted the workings of grace, and so she has been raised by God's grace to highest place of all God's creatures. She is the Mother of God, Queen of Heaven and earth, the House of God and the Gate of Heaven. All generations shall call her uniquely blessed among women.
So on the feast of the Presentation of Mary, let us entrust ourselves and our intentions to her, as God the Father entrusted His only begotten Son to her so long ago. Let us ask her intercession for all the graces we need, and ever return to her help and protection in the midst of our struggles to discern and obey the will of God.