As $ n$ approaches $ \infty$, the terms get very close to each other. So for very large $ n$, $ (n + 1)a_{n + 1} = na_{n}$ => $ (n + 1)a_{n}(1 - a_n) = na_n$ => $ n = (n + 1)(1 - a_n) = n + 1 - na_n - a_n$ => $ (n + 1)a_n = 1$ But for sufficiently large values of $ n$, $ n + 1 \sim n$, so $ \lim_{x\to\infty}na_n = 1$.