You could ask the question of St Paul, but he has already written:
I was given a thorn in my flesh, a messenger of Satan, to torment me. 8 Three times I pleaded with the Lord to take it away from me. 9 But he said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” Therefore I will boast all the more gladly about my weaknesses, so that Christ’s power may rest on me. 10 That is why, for Christ’s sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong." 2 Corinthians 12 7-10
And Mark wrote in his Gospel:
"Watch and pray so that you will not fall into temptation. The spirit is willing, but the body is weak."Mark 14:38
St Therese of Lisieux, a Doctor of the Church, wrote:
Saint Therese of Lisieux encourages us in our attempts towards holiness in our vocation to love and serve. Of her own response to the call, she wrote, “This desire could certainly appear daring if one were to consider how weak and imperfect I was, and how after seven years in the religious life, I am still weak and imperfect. I always feel, however, the same bold confidence of becoming a great saint because I do not count on my own merits since I have none, but I trust in God who is Virtue and Holiness. God alone, content with my weak efforts, will raise me to Himself and make me a saint, clothing me in His infinite merits. I didn’t think then that one had to suffer very much to reach sanctity, but God was not long in showing me this was so and in sending me the trials I have already mentioned.”
In response to a novice who was discouraged by her faults, Therese said, “You make me think of a little child that is learning to stand but does not know how to walk. In his desire to reach to top of the stairs to find his mother, he lifts his little foot to climb the first step. It is all in vain, and at each renewed effort he falls.” “Well, be like that little child. Always keep lifting your foot to climb the ladder of holiness, and do not imagine that you can mount even the first step. All God asks of you is good will. From the top of the ladder, He looks lovingly upon you, and soon, touched by your fruitful efforts, He will Himself come down, and taking you in His arms, will carry you to His Kingdom never again to leave Him. But should you cease to raise your foot, you will be left for long on the earth.”
To another, Therese said, “You want to climb the mountain, whereas God wishes you to descend it. He is awaiting you in the valley of humility.”