中国古典文学 has the preface.
Here's the first paragraph:
初刻拍案惊奇
凌濛初
序
语有之:“少所见,多所怪。”今之人,但知耳目之外,牛鬼蛇神之为奇,而不知耳目之内,日用起居,其为谲诡幻怪非可以常理测者固多也。昔华人至异域,异域咤以牛粪金;随诘华之异者,则曰:“有虫蠕蠕,而吐为彩缯锦绮,衣被天下。”彼舌挢而不信,乃华人未之或奇也。则所谓必向耳目之外索谲诡幻怪以为奇,赘矣。
The translation of “To one who has seen too little of the world, everything is strange.”
is:
少所见,多所怪
There is also an entry for this in ABC Proverbs which says:
Lit [Things (which are)] seldom seen [are felt to be] strange.
Note Cf. the preface to Chū Kè Pāi'àn Jīngqì; now more commonly said shǎo jiàn, duō guài; see also the preceding entry.
Like the definition mentions the more, modern, common variant of this phrase is 少见多怪 which ABC defines as:
The less one has seen, the more one marvels.
ABC Proverbs also contains the old phrase with an added sentence:
少所见多见怪,睹橐驼谓马肿背。
Lit [One who has] seen little regards many things as strange; [(s)he] sees a camel [and] calls [it a] horse with a hunchback.