Psycholinguists are divided on the answer, but they agree on several points. For starters, a 2-year-old’s brain has a substantial neurological advantage, with 50 percent more synapses — the connections between neurons — than an adult brain, way more than it needs. This excess, which is an insurance policy against early trauma, is also crucial to childhood language acquisition, as is the plasticity, or adaptability, of the young brain.

Once the “critical period” — the roughly six years of life during which the brain is wired for learning language — is over, the ability to acquire a first language is lost, as your brain frees up room for the other skills you’ll need as you mature, such as the ability to kill a wild boar, or learn math, or operate your iPad.

Another advantage a toddler holds is his very lack of experience. After speaking our native language for decades, we adults can’t help but hear the second language through the filter of the first. And this filter doesn’t take decades to develop. Researchers have found that newborn Japanese babies can distinguish between the English “L” and “R” sounds, but if not exposed to Western languages, they begin to lose that ability — not by the age of 6 or even 3 — but by eight months.

Adult language learners are, to borrow a phrase used by some psycholinguists, too smart for our own good. We process too much data at once, try to get everything right from the get-go and are self-conscious about our efforts. But toddlers instinctively grasp what’s important and are quite content to say, “Tommy hitted me,” as long as Tommy gets what’s coming to him.

All this means that we adults have to work our brains hard to learn a second language. But that may be all the more reason to try, for my failed French quest yielded an unexpected benefit. After a year of struggling with the language, I retook the cognitive assessment, and the results shocked me. My scores had skyrocketed, placing me above average in seven of 10 categories, and average in the other three. My verbal memory score leapt from the bottom half to the 88th — the 88th! — percentile and my visual memory test shot from the bottom 5th percentile to the 50th. Studying a language had been like drinking from a mental fountain of youth.