not know any better

not know (any) better

1. To not have the knowledge or development to behave correctly or make an informed decision. Don't get so mad at him for writing on the walls—he's two, he doesn't know any better.
2. To not have (contradictory) information about something. Used in the construction "if I didn't know (any) better" to sarcastically or ironically suggest that something is probably or obviously the case. If I didn't know better, I'd be inclined to believe that these megacorporations don't actually care two figs about consumers. Say, if I didn't know any better, I'd think you were actually enjoying yourself, just like I said you would!
See also: better, know, not
Farlex Dictionary of Idioms.

not know any ˈbetter

not behave well, politely, etc. because you have never learned how to: You can’t blame him for his bad table manners; he doesn’t know any better.
See also: any, better, know, not
Farlex Partner Idioms Dictionary
See also:
  • do unto others
  • be behind the times
  • bang (people's) heads together
  • bang people's heads together
  • bang your/their/our heads together
  • act out
  • play to the gallery
  • play to the gallery, to
  • be on the same wavelength
  • be on the same wavelength/on different wavelengths
References in classic literature
He was very young, and did not know any better. Mrs.
I do not know any better qualifications for a friend and companion."
She was twelve years old and did not know any better. Mapuhi relieved his feelings by sending her reeling from a box on the ear; while Tefara and Nauri burst into tears and continued to upbraid him after the manner of women.
We were cheated by Boko Haram as we did not know any better.
He soon graduated to armed robbery because he did not know any better.
'If we did not know any better, the message sounded like [Hun Sen] because he is a leader who [speaks] clearly, sharply and straight to the point."
The hapless consumer who did not know any better end up losing his car and credibility, the auto dealership ends up with an unhappy customer, and the bank is left holding the bag and probably will end up losing money in disposing of the foreclosed vehicle.
Unfortunately the political engineers do not know any better. They only believe in witch-hunts.
Now Bancroft has detailed the events in Cape Town in March this year, telling Fox Sports he did not know any better and just "wanted to fit in and feel valued".
This social stigma that existed around psychiatry centred on the manner in which mental patients had been previously treated in society, where they were unfortunately forced into straitjackets and locked up in asylums, or sold to circus shows by families who did not know any better. Any affliction of the mind, after all, was previously termed as madness, and people unfortunately thought that mental patients were just that -- mental.
A hapless truth is that impoverished labourers will continue to make the same basic mistakes without any intentions of doing so for the reason that they do not know any better. Resolving this situation is a long-term task but it critically highlights the requirement for standardising and formalising, to some degree, training for jobs that require skilled labour.
There is a horrific gap between the elite and the disadvantaged in Ekiti and if there is one person who knows how to exploit it, it is Ayodele Fayose, setting the elite against the disadvantaged in society and setting himself as the champion of these people who often do not know any better what is happening to them.
'Then, why not go after the syndicates, the adults, not the children who do not know any better and are vulnerable?'
But as he wrote he started thinking the boy probably had been brought up to think being gay was unnatural and did not know any better.
Just as I did not judge Mary, we can't judge parents who are deceived because they did not know any better or could do no more.