God is His infinite wisdom know exactly what adversity we need to grow more and more into the likeness of His Son. He not only knows what we need but when we need it and how best to bring it to pass in our lives. He is the perfect teacher or coach. His discipline is always exactly suited for our needs. He never over trains us by allowing too much adversity in our lives.
From Trusting God by Jerry Bridges page 128
And we know that in all things God works for the good of those who love him,
who have been called according to his purpose.