With the textwidth option set the text written can be wrapped when we leave insert mode. If I type a line longer than my textwidth value then it will go on a new line. e.g. with set textwidth=5 and set linebreak :1 2 3 [4]1 2 34[]lorem ipsum dolor[Esc]lorem ipsum dolor[][X] means: I press X where [] is.So when entering a line of number spearated by space, at the moment I enter the 6th character (in this case the number 4) the line break.But when I enter a sentence the line doesn't break until I quit insert mode.Do you know what I can try/set ?
Breaks line without leaving insert mode
insert mode;line breaks
So as we troubleshooted in the comments the problem came from the formatoption value.According to :h formatoptions :This is a sequence of letters which describes how automatic      formatting is to be done.Your settings contained the letter l which according to :h fo-table does the following:Long lines are not broken in insert mode: When a line was longer than      'textwidth' when the insert command started, Vim does not      automatically format it.So the solution is to use the following command set fo-=l. Still according to the doc it is better to use the += and -= features options of set to avoid conflicts with tags added later.Another important point is how these tags are set: a lot of filetypes set those tags automatically. For example in [path_to_vim_installation]/vim74/ftplugin/c.vim you can read: Set 'formatoptions' to break comment lines but not other lines, and insert the comment leader when hitting <CR> or using o.setlocal fo-=t fo+=croqlA solution is to override those behavior in your .vimrc for the filetypes that you want.