Although a Pineco's life is long by the standards of bug pokemon, like human life it is finite. Pineco live most of their lives hanging onto or bouncing across trees, growing larger, until they can no longer hold on, drop to the ground, and explode to their deaths. Pineco are remarkable, however, in that they can escape death through evolution, for the mechanized body of a Forretress does not age and can survive many blows, even its own explosion, and can only be slain through fire.
Pineco are even more remarkable in that, although many grow powerful enough to have the opportunity to evolve and live forever, they are sharply divided on whether to actually do so. For Pineco, evolution is an enormous dilemma fraught with indecision. Forretress are a species of great procrastinators, robbed of any urgency in life by the fact of an eternal tomorrow, and they waste away in hedonistic, often vicious pleasures like laying spikes in the forest and making other pokemon walk across them while they shoot gyro balls at them. Nor does refusing to evolve mean immediate death, and when at death's door, it is often too late for evolution.
Whichever decision a Pineco makes, it is often fraught with regret. The forests where Pineco grow do not burn easily, and many Forretress, unable to simply explode, go on long journeys in search of fire. And although the dead can not voice their regret, the old, weak, and dying often wish for evolution in sheer terror at the thought of their life's end.