Once, alone and a little lost in the London subway, I said thank you when a nice guy helped me figure out where to go. In response, he leaned in to hug me, held me close for a few stunned seconds, slid his hands down and squeezed.

In my imagination, this is the part when I say something sharp enough to remind him that this is not his dance space. In my imagination, it comes out without a waver or a hint of a smile. In real life, during those three seconds that felt like 30, nothing came out at all. He smiled, turned and left me wondering if I had just dreamed the whole thing.

I’d accepted this sort of thing as the price of being female in public, a fact of life like rush-hour traffic. My anger, whether about a handsy hug or a co-worker telling me to keep my mouth shut after I told a joke he didn’t like, had turned into background noise, and I got good at ignoring it. Acceptance seemed more evolved than rage, and no less effective. I’d learned to step aside, to swallow my replies instead of spitting them back.

So when I signed up for a self-defense class, after receiving a gift certificate for my 21st birthday, I didn’t expect much. Until then, the best defense advice I’d gotten was to carry an umbrella around, “just in case.” The fun part: I learned to hit hard. Our instructors, suited up in full-body protection, taught us what it felt like when resistance landed where it meant to. But the physical fighting — our elbows launching into their faces and our knees hitting between their legs — wasn’t the only thing that made those hours in the sweaty New York studio so cathartic. The part that sneaked in deeper was the idea that I had a right to defend myself at all, with my limbs or my voice.

The opposite message had seeped in and crystallized over the previous years. Between the socialized niceness of my gender and the lingering effects of once being the new kid with a bowl cut and no English, I got used to being artificially timid. I’d held myself back from being the loudest I could be.

That’s why the hardest part of the training was also the quietest.

One at a time, each student would stand with an instructor in front of the class. The teacher would start an interaction as a pal or co-worker, doing homework or going for ice cream or planning a meeting. At some point, the instructor would put a hand on the student’s shoulder and keep it there, a symbolic move to represent discomfort. It should have been easy to push back. The stilted formality of the script — “I feel uncomfortable when you put your hand on my shoulder; please stop” — was easy to laugh at, until I couldn’t get the words out without smiling or apologizing. In other scenarios, when our teachers played pushy strangers, the grim silence that followed “I don’t want to talk to you” felt as heavy as the blows I’d landed earlier in class.

With my friends, directness came naturally. But given the opportunity in a classroom role-play to say aloud what I wanted, I shrank. It felt unnatural, even aggressive, to point out anything short of egregious. Habitual niceness meant habitually nicked boundaries, dismissed as just more dents in an already beleaguered autonomy. “Sorry” crept in, even though I wasn’t.

Numerous studies identify gendered challenges to making oneself heard. In 63 studies on talk between men and women in different contexts, men talked more than women in all but two, a pattern that starts as early as kindergarten. Women are almost comically more likely to be interrupted than men — in one examination of cross-sex conversation, men did 98 percent of the interrupting. Medical professionals tend to be more skeptical of women who complain of pain. Police departments routinely disbelieve, discount and dismiss women’s reports of rape.

Charlene Senn, author of a 2015 study in the New England Journal of Medicine on sexual assault resistance training for first-year female college students, says verbally delineating boundaries is tougher for most women than fighting an attack. “It activates our realization that this person is someone we know,” she says. “And in those moments, the socialization that many girls and women get to be nice, to make people socially comfortable, to not upset people or hurt people’s feelings, to care how people will react — all of those things get activated.”

A Justice Department study focusing on college-age women showed that the majority of sexual assault offenders were known to their victims, so Senn’s training program focused exclusively on acquaintance scenarios. It included lessons in detecting risks and overcoming emotional obstacles, in addition to a physical component. Senn says the key in her training is uncovering what’s been suppressed, “taking women’s gut instincts . . . and saying: ‘Yep, you’re right about that. You don’t need to dismiss those ideas. Those are good instincts that are telling you there’s something off about this situation. Trust them.’ ”

Perhaps unsurprisingly, the study found a connection between such training and reductions in completed sexual assaults over the following year. But students in the training group reported fewer attempted assaults, too. A possible explanation, Senn says, is that students caught warning signs earlier. Taught to notice red flags, they were able to stop a relationship or an interaction. “We’ve heard from other women that they felt stronger in their whole being, and that doesn’t just mean physical strength,” Senn says.

I felt the same way. The invitation to stop ignoring my own small voice — to let it get bigger — echoed in every part of my life. Learning to defend myself against the worst-case scenarios taught me how to move through the world the rest of the time.

Walking fast on crowded sidewalks, I started saying “Excuse me” — a request — instead of “I’m sorry” — an apology. Small as they are, the words trickled in deep. When a teenager in my neighborhood responded to my friendly hello by staring and stroking my arm as he passed me, my anger didn’t just freeze my smile; it whirled me around to shout after him to keep his hands to himself. When a man asking for $2 for gas hurled insults after me one night, then asked again the next night without a blink of recognition, I could interrupt him to say I wasn’t going to listen. I didn’t have to yell and hit to say no; I could just tell him.

Here’s the thing about that big little word, “no”: It makes room. You say no and burn out the underbrush choking your growth. You make space for getting bigger. And you don’t even know how much room you have, how big you can get, until you do.