Making the browser windows narrow is a bad suggestion. Because most websites have some sort of navigation bar on the left and another bar on the right, so we need a wide enough window to get enough of the main text (width).

There are very few websites without those columns.

Surely between the browser window too wide (where the text lines are too long) and the browser window too narrow (where side bars are hidden) there exists a width that is exactly to your liking.