Our difficulty in completely trusting God, and following His Will, stems from our own human brokenness. The wounds of our existence have hardened our hearts and the full trust of a child have long left our lives. And only God can make us whole again, slowly, bit by bit, each day, each moment. Our only job is to cooperate.
If God gives, accept. If He takes, let go. No fuss. No rolling on the floor crying and kicking. There is nothing in this world worth more than following His Will.
Humility is knowing very well what we can and cannot do, without closing the possibility that with God's specific graces something more can be achieved. But all these shall be according to His Holy Will.