There are basically four ways to misunderstand Buddhism. Master Dogen mentions all of them in Shobogenzo.
The first is called naturalism. If we believe that we are buddha no matter if we practice the Way, no matter if we attain the truth, no matter if we learn Buddhism from an authentic teacher, this is called naturalism. It is a very superficial, very silly understanding of Buddha's truth. So it is definitely not understanding Buddha's truth. Even if we ask: Who is not a buddha? And even if we cannot find a single person or single thing, which is not a buddha, still it is not Buddha's teaching to conclude that everyone is a buddha, so the whole of Buddhism is useless or that practice is not necessary. Of course, everyone and each thing is a buddha, but what does it mean?
The second misunderstanding is the belief that every person possesses some kind of bright, spiritual intelligence which is different from the form of our existence. Even these days some people believe that we have some kind of hidden spiritual essence that we can discover and then show it to others. But true Buddhism says that this very body and mind, this ordinary person and their everyday actions show our Buddha nature completely and nothing is hidden. Moreover, our true self is not something hidden, or separated - it is not limited by mind, by body or by the world outside. It is just our everyday life and winter leaving and spring coming. It is really something amazing, but it is amazing because it is independent on limited ideas of people. Just like mountains get along with storms and snow, the universe doesn't fight a true self, nor does it give a person their true self. As we cannot point to the universe itself, we cannot point to one's true self. Still, this doesn't mean that there is no universe or no true self.
The third misunderstanding is the belief that the goal of our Buddhist efforts is to attain some kind of great personality and then show to others how great we are. The others will see that we are better than others and will want to learn from us how to become such a great person. In fact, we practice the Way despite having been a buddha ever since the beginning of the universe and despite getting more or less what we have always had. So even if there is no profit or gain in practicing the Way, we can notice all our Buddhist ancestors practiced and studied the Way as if it was the most important thing ever. Just like storms make noise as if storms were the most important thing ever, just like rabbits fight in the fields as if only rabbit fights mattered, just like flowers bloom in the spring as if only flowers could change the universe, buddhas practice the Way without thinking about their past or future, and they practice and study the Way as if nothing else was important. To practice the Way without comparing it to other ways or secular values is just like a branch cracking in the woods. It doesn't think it should crack, it doesn't think it shouldn't crack. It doesn't think cracking is empty and it doesn't think cracking is loud. It doesn't think there is some kind of spiritual essence to cracking. It doesn't crack to become a buddha. It just cracks.
The fourth misunderstanding is to make Buddhist practice and philosophy something stuck and solid, like a bar of soap in the bathroom. We should not discard Buddhist practice and philosophy, but we should not make it something solid and rigid, like a bar of soap. We should freely give bars of soap and accept bars of soap. We should let practice come and go. I don't mean practice zazen three times a year, I mean practice zazen when it is our habit to practice, and it should be every day, and stop practicing zazen, when it is our habit to stop and go to bed or begin eating. We should let Buddhist ideas and values come and go. If we stick to practice and make it a very important part of our lives, it becomes something separate and loses its original value. If we make Buddhist philosophy a special thing and we think about it all the time, it loses its original meaning and becomes rigid, so it cannot help anybody. To transcend buddhas, to let go of buddhas, to let buddhas come and go, to forget buddhas and witness cracking branches, that is the way of those who have transcended Buddhism and buddhas, while practicing zazen regularly and bowing with others and eating with others over and over again.