Because learning a formal language is akin to learning a programming language. You misunderstood education as formal education. Just by exploring as a child, a

Because learning a formal language is akin to learning a programming language. You misunderstood education as formal education. Just by exploring as a child, and living, you learn your native language. Before a child goes to school, they already learn by playing. That, too, is education, and sadly some children are deprived from that or their lack of intelligence already shows. Our oldest (not even 3), for example, is well ahead language-wise, whereas motor skills she's a tad behind. If you don't practice something, the skill tend to get lost, yes. However, something you learned at a very young age defines you, and is (for good or bad) difficult to unlearn. Only at an old age or due to memory/brain related disease does it get lost. When I went on vacation to USA for 3 months, twice, I had to speak English. I didn't speak Dutch at all. When I got back, I had to adapt to Dutch way of living and Dutch language, but it went rather quick. I have no problem 'thinking' in English because I learned this at a very young age; whereas French just never clicked with me. These people who end up with expat parents and the like are an exception. Exceptions like these prove the rule.