Still Human

3. There are no mistakes, only lessons. Growth is a process of trial and error, experimentation. The "failed" experiments are as much a part of the process as the experiments that ultimately work.

Donatello is a scientist. He, by nature, is always doing experiments, tinkering with the household appliances, or putting together cool inventions from junkyard scraps.

His father and sensei, of course, knows about how many old things get turned into new things. He is also the only one aware of Donatello's frustration when he fails.

When he was younger, Donnie thought of his failed experiments and inventions as mistakes, nothing more. They were errors in his data, and he couldn't let them stay. Splinter, however, told him that the mistakes are important too. You have to learn from your mistakes, not just brush them aside, or else you'll be doomed to repeat your mistakes over and over again.

He takes that lesson to heart, now. Dozens of trials with retro-mutagen finally produced a viable product, and April's father was saved because of it. New inventions like his glider wings and zip lines and the Shellraiser help his brothers stay alive on missions and get everything accomplished.

The one thing he hates to think of as a mistake is Metalhead. Metalhead, who saved his brothers and all those other mutants; Metalhead, who let himself get blown up so that Donatello could live.

He was not a failure, no matter what his brothers had said about his earlier designs. But he wasn't really an experiment, either.

Artificial intelligence meant Metalhead had known what he was doing…known, but done it anyway. It nearly killed Donatello to think of it.

He couldn't think about it now, though. Metalhead could wait. Others like Timothy and Malachi and even Baxter and Bradford and Xever needed retro-mutagen cures as soon as possible.

Metalhead went into a box called "To Be Restored" instead of the "To Fix" box. He didn't need fixing. He just needed to be put back together again.