"Once bitten, twice shy", what does that mean?

having gone thru a traumatic thing u never ever mean to see again

This idiom depicts a situation when someone goes through a bad experience at a certain place or a certain thing or with a certain person, he'll avoid it in the future.

Example:

Travelling in the bus was terrible, I'll not do it again, Once bitten twice shy.

it means that someone who has been hurt or who has had something go wrong will be far more careful the next time