I’ve noticed that the most mature and accomplished developers I’ve worked with are also those who most frequently say “I don’t understand” when they’re listening to a technical explanation. This has been the case with coworkers both at Fog Creek and at Khan Academy.
In one way, it’s counterintuitive. Shouldn’t the senior devs already know everything? But it makes a lot of sense. Those who are most secure in their own abilities are the most comfortable to admit when they haven’t fully wrapped their minds around something. Newer devs assume that their confusion is their own fault. They don’t want to interrupt others due to their own perceived shortcomings.
"I don’t understand" is the perfect response. You’re not insulting anybody. You’re not showing weakness. You’re building a culture of respect for how smart everybody is, because you know that after a few minutes of explanation you will get it.
Either that or you’ll find a bug. I like to think of “I don’t understand” as a kind of reverse rubber ducking. Except in this version, the duck comes alive and quacks and stomps and “I don’t understand”s all over your keyboard while forcing you to explain various things.
It’s most said by the best, decades after they’ve become a master. We newer devs should follow their lead and get rid of any stigma associated with those words.