David F. Sandberg believes "there is always room for improvement" in directing.

The 39-year-old filmmaker has helmed the DC Extended Universe flick 'Shazam!' and horror movies such as 'Lights Out' and 'Annabelle: Creation' during his career and believes that "dedication" has been a key factor in his success behind the camera.

Speaking in a YouTube video entitled, 'Can You Be An Introvert Director?', David explained: "There's always room for improvement. And how do you improve at something? By doing it over and over and over.

"You start out making really s***** movies but you keep at it and as the years go by the movies get a little less s*****.

"Dedication can often make up for a lack of innate talent. But that's the tricky part. Not the learning. The dedication. Not giving up. Because progress isn't always linear."

David continued: "There will be moments where what you're making is worse than what you made before and it feels like you're going backwards but that's OK. Even in those moments you're learning things that might be useful later on. Or you're learning what just doesn't work for you. Experience is never a waste."

Sandberg made a voice appearance cameo in the post-credits scene of the first 'Shazam!' movie and explained how it was decided just to keep his voice in the final edit.

He said: "I actually gave the whole project that I made to the sound designers and like, 'Just use this. Don't change anything.

"You just sort of fall in love with a certain thing, and then you just can't, in your head, change it. So it's like, 'Yeah, we'll just keep my temp voice in there.' "