Using flashbacks to highlight a past event or emotion to enforce the gravitas of the mood or situation. There is nothing innately wrong with flashbacks. Some writing instructors will say, a flashback is a mortal sin, but a flashback is a bad thing if it’s dull. The first mistake is using bland narrative summary flashbacks as if they’re in a hurry to return to the main action. If the back story is relevant and worth presenting in the first place, then it should probably be dramatised and vivid as the principal ongoing activity. The other mistake is writing flashbacks that are unnecessary; in other words, they give back story that just isn’t needed—dull stuff better left unsaid. The good thing about flashbacks is that it allows you to show background information that is relative to the story, without info dumping. In summary; only use flashbacks to impart knowledge to the reader that they need to know to understand the story course.
1, Is this event or emotion essential to understanding the plot or characters?
2, Is this the most efficient way to reveal this information?
Your answers should be a definite yes to both of those questions.