There are of course many naturally talented and driven kenshi who start strong and continue to improve at the optimum speed throughout their kendo careers, taking seventh dan in their late 30s, hachidan in their late 40s and continuing on to become the grand old men of our kendo community.
In the west, where many of us start as adults, there are those who appear to be naturally talented. Despite the odd nature of kendo movement, they race up the ladder to 2nd or 3rd dan, leaving many of their peers to struggle and make far slower progress. It is often these quicker learners who give up when improvement starts to become more difficult later in their kendo career. This can happen at many levels and I have seen people drop out after achieving fourth and fifth dan, in several cases 6th dan, where the pressure of making the next step seemed too difficult.
A number of kenshi will cheerfully admit to enjoying the fighting aspects of kendo and not being particularly worried about improving technique. They like the idea of putting on armour and clashing shinai for a few hours a week. Most dojo have members like this who keep the club funds topped up and play an important part of the life of the club, but do not see kendo as a sugyo.
I have watched others who are dedicated to learning correct kendo, who find every aspect a challenge. They return to the dojo week after week, struggle with the intricacies of footwork, breathing, cutting action and with uniting them all in ki-ken-tai-itchi . They cheerfully continue their training over a period of many years. Often these individuals spend many years slogging up the grading system, taking repeated attempts to pass each level.
Many of these slower starters do reach a stage where everything falls into place and their pace of progress changes completely. It might be that they reach an understanding of a single element of kendo such as correct breathing and everything else becomes clear. It may not be in the form of a dramatic epiphany, but one day a bad habit disappears and one correct action leads to another and 6th and 7th dan no longer seem unattainable.
Whatever our learning speed, kendo thankfully gives us plenty of time to correct our faults.