D. Martin Lloyd-Jones writes about the tendency that some believers have to become discouraged because their Christian lives are not progressing at the pace they would like (in his book, Spiritual Depression.) Lloyd-Jones likens the need for maturity in this area to that of a child (I pictured a toddler) who takes off running out the door...but we know that the child cannot run very far.
Taking Lloyd-Jones' analogy a bit farther, compare the running of a seasoned, adult runner with the childish energy of the little toddler. If we did not know better, we might expect that the child would "outrun" the adult when we see the child's unbridled enthusiasm and effort. Yet, we all know that the average adult would surpass the child if not very quickly then at least soon in the race, even if the adult were only to walk.
The analogy is made to demonstrate that error in thinking that many Christians develop at some point in their lives, and which, if left alone, may dominate their thinking and be a constant source of discouragement. Consistency in growing in godliness is to be valued more than sudden spurts of spiritual excitement. Most people, however, can look back to some "spiritual high" that they experienced along the way and become discouraged that they have not subsequently encountered a comparable period in life. In reality, the individual's growth spiritually is better measured by his/her daily growth in God's Word and in prayer. These growths are usually immeasurable, but it is this type of growth which produces spiritual maturity.