Initial D taught us many lessons of life. When Takumi pushed the 86 to its absolute limit and consequently blew the engine in Second Stage, Bunta told him it was impossible to fix it, it was just beyond repair. Takumi refused to accept the reality by saying if the 86 received a new engine, it won't be the same. If we apply that same analogy to real life situations, it is clear to see that the author is trying to convey the message of letting go. Sometimes we mature through letting go. If Takumi never let go of that mentality, he would never grow out from that. The rest was history.