Last month, on a flight to a friend’s wedding in Chicago, I sat next to someone even more clueless about weddings than I was: one of my fellow bridesmaids.

“I bought these great open-toed sandals,” she cooed. “They match the dress perfectly! How about you?”

Hmm, didn’t she get the e-mail from the bride insisting we wear closed-toe pumps? Turns out she hadn’t gotten her dress altered either (“It’ll be fine!”). Plus she’d forgotten to RSVP to some of the wedding-weekend events. And she was shocked to hear that I’d gone to the trouble of preparing a toast for the rehearsal dinner. In short, she was a disaster. But I had to smile. She was just like I used to be.

Before I got engaged last May, I’d broken every rule of wedding thoughtfulness. It wasn’t that I didn’t care about the bride and groom or that having good manners wasn’t important to me. I consider myself a caring friend: I send thank-you notes promptly, I never show up to a housewarming empty-handed. But somehow, the world of proper wedding behavior had eluded me.

It wasn’t until I started receiving piles of lovely engagement presents (before we’d even decided to have an engagement party) that I realized I should have given some myself. And it wasn’t until my own bridal shower, when friends who couldn’t attend made sure they still had gifts waiting for me at the hostess’ home, that I learned I should’ve done so, too. I’d actually arrived at one friend’s “game theme” shower with a waffle maker. She’d opened it, paused, and politely said, “Well, this will be a lot of fun to play with.”

I never bought off the registry, reasoning that personal gifts like, say, monogrammed robes, were more exciting than china. “What an original idea,” brides would write in their thank-you notes. Now, after spending hours selecting items for my own registry, I find myself slightly miffed when guests don’t use it. Why do they think I’ve gone to all that trouble? And that idea that it’s acceptable to send gifts up to a year afterward? No one told me that, though technically acceptable, procrastinating until months after the wedding is disappointing for the bride and groom.

Occasionally, I’d forget to send in the response card until the bride’s mother followed up. At the time, I didn’t see the big deal. After all, I’d told the bride a million times I was coming! Now, after eagerly awaiting the mail each day so I can tear open those little cards and begin table arrangements, I marvel at my thoughtlessness. With the wedding a month away, I can’t remember my vows, let alone which friends told me what. And when guests ask to bring dates, I bristle. Our numbers are so tight I couldn’t invite some of my cousins. How could I squeeze in someone’s new flame? But then I recall how once, days before a wedding I was in, I begged the bride to let me bring my new boyfriend — of six weeks.

“Fine,” she snipped. “If it’s really that important to you.”

I spent the entire wedding locked in his arms, neglecting my bridesmaid duties. Soon after, the boy was history, but I’m reminded of him and my poor judgment whenever I see the two of us in my friend’s wedding photos.

Ultimately she got over it; perhaps she’d committed her own faux pas, too, before she was a bride. Or maybe she just preferred to focus on the ways her day was special. I’m mortified by my past behavior, but thankful that this friend and others let it all slide. And now that I’m in their position, I’m trying to do the same. Don’t get me wrong: Having to e-mail guests for their RSVPs makes my blood boil. But I know that someday they’ll be brides and grooms themselves and discover that there are actually pretty good reasons behind those wedding rules we’ve all (cluelessly) broken.