A gray-brown Taiwanese macaque screeched. Then a human. I turned to see a monkey loping after a student who stabbed backward through the air with her red polka-dot umbrella. She hugged a plastic bag of food to her chest like she was holding an infant. Finally, the macaque retreated.

Welcome to a typical day on the Sun Yat-sen University campus in Kaohsiung, Taiwan. I was chatting with one of my classmates, Kevin, as the battle raged between my fellow human and our hairy relative. Kevin was 28, Canadian, tattooed and hollow-eyed, the way people who party too much (or used to party too much) look. Where I used to bartend, it’s how my co-workers looked if they’d been there for more than five years. Age-inappropriate wrinkles frame their lively eyes.

I remember Kevin because I was 19, and he was saying he didn’t like to party anymore. To my 19-year-old brain, this was incomprehensible, as if he’d just said, “I gave birth to triplets!” Was I supposed to congratulate him? Now I realize it’s distinctly possible to party too hard, for too long. Not that there’s anything wrong with letting loose after another long semester. Even if it involves alcohol, and maybe some coke, and maybe some naked dancing on tabletops. Or not.

What’s more important is remembering the bigger picture, because the final stages of brain maturation occur in our 20s. The prefrontal cortex, responsible for executive functions such as decision-making, planning and prioritizing, matures last. That means our developing brains are uniquely vulnerable to poor decisions exactly when we’re most likely to make them. It’s incredible that any of us graduate at all, much less from Cal.

Maybe all those real adults who call us “adultescents” are not entirely wrong, when our brains don’t resemble adult brains functionally or structurally until age 25. What I want to know is, how did rental-car companies figure it out before everyone else?

In a recent study published in Neuron, University of Oxford scientists found remarkable similarities between humans’ and monkeys’ ventrolateral (left-front) prefrontal cortex. The key differences? Humans have an egg-sized region that constantly evaluates how good the decisions we haven’t made are, so we can figure out alternative ways of doing things and switch course, if necessary. Also, the part of our brain that processes auditory cues (the temporal cortex) connects to this prefrontal cortex, whereas in monkeys, it’s more strongly connected to emotional regions.

In some ways, teenagers and young adults are a lot like monkeys. We can’t be held accountable for our impulsivity and poor decisions. We simply lack the biological hardware. Yet, the decisions we make now matter. They have implications for our lifetimes, not just for our careers but for the people we become. I can’t down five shots daily like when I was working at the bar because, well, it’s no longer free, but also because regular drinking is associated with lower performance on memory tasks and a smaller hippocampus, a region that’s fundamental for learning and memory. Is that why I have trouble remembering things now? Is this a normal part of getting old? Or did I drink too much? The science is somewhat sobering.

And what about other substances’ effects on our developing brains? What does it mean to lose our sense of self before we’ve even developed one? I can’t help thinking of one friend from Santa Cruz with dirty-blond surfer hair, the sweetest smile and more brains than were probably good for him. He was a philosophy major and a psychonaut. Eventually, he started coming up with conspiracy theories about the government, about the University of California (maybe not entirely unfounded) — about everything. Then he left Berkeley, changed his phone number, deleted his Facebook; and all that’s left of him (at least in Berkeley) is the people who remember him and a list of all the drugs he’s ever done scribbled on a co-op basement wall. I like to imagine he spends his days reading philosophy and snowboarding now, but I can’t be sure.

I’m not advocating for everyone to retreat to the nearest Buddhist temple to shelter our vulnerable minds from everything that might hurt them, from stress and sleep deprivation to abusive relationships and substances. But it wouldn’t hurt to picture our brains as delicate plants, about to flower. We wouldn’t water a houseplant with beer (at least I hope not, because the yeast might start growing in the soil, and the plant needs some complex carbs, not simple sugars), so we shouldn’t water our brains with beer. Apparently, beer makes good slug traps, though. You just leave some out in a dish, and slugs will crawl into it and die. Not what we want our brains to do.

All I’m saying is, we (and our professors and GSIs) ought to cut ourselves a little slack when we show up an hour late to a final or sleep with that person we said we’d never see again. Our forebrains couldn’t do any better. But it doesn’t mean they shouldn’t try.