Preguntas Indecisas
How do you use 如此 (ruci)? Is it the same as 那么 (name) or 这么 (zheme)?

如此is more often seen in literature, formal situations, written Chinese, etc.
If someone say (by say, I mean spoken Chinese)你怎么如此笨, it sounds a little geeky.

In our daily life, 这么and那么are more commonly used.
你怎么这么聪明？ 这to you
他怎么那么聪明？ 那to others

"如此" is less 口语化 than "这么" and "那么"
so although 你怎么这么笨 = 你怎么如此笨 is true, we seldom say "如此" in spoken Chinese.