Speaking to students at the University of Houston, McConaughey drew closely on his first film role, in Richard Linklater's 1993 cult classic Dazed and Confused, to explain why "a process of elimination" is necessary when young people are trying to forge their own identity.

In his address, which has been published in full by Time, McConaughey said he thought his character David Wooderson should not have appeared in some parts of the film.

"In 1992, I got my first job as an actor. Three lines, three days work, in a film called Dazed and Confused," McConaughey, 45, began.

"The director, Richard Linklater, kept inviting me back to set each night, putting me in more scenes which led to more lines all of which I happily said yes to. I was having a blast."

McConaughey told the students that, although he appreciated the extra screen time – and extra money – at the time, he recently rewatched the film and realised he really should not have been in some scenes.

"In one of the scenes, I exited screen left to head somewhere, then re-entered the screen to 'double check' if any of the other characters wanted to go with me. Now, in rewatching the film, (and you'll agree if you know Wooderson), he was not a guy who would ever say, 'later', and then come back to 'see if you were sure you didn't wanna come with him ... '," he said.

"No, when Wooderson leaves, Wooderson's gone, he doesn't stutter step, flinch, rewind, ask twice, or solicit, right? He just 'likes those high school girls cus he gets older and they stay the same age'."

The actor, who won an Academy Award for his role in Dallas Buyers Club in 2013, said the character presented a lesson in knowing when to say no.

"It's just as important where we are not as it is where we are," he later added.

Although he was raised in Texas, McConaughey did not attend the University of Houston.

He studied radio, television and film at the Austin College of Communication within the University of Texas, graduating with a bachelor's degree in 1993.

McConaughey had originally planned to follow his undergraduate study with a law degree, although he lost interest.

"The family always said, 'Yeah, you need to become a lawyer and then come and get us all out of trouble'," he told Texas Monthly in a 1996 interview.

"But it wasn't tickling my gut. I wasn't waking up every day thinking, 'Man, I can't wait to get to law school"."

Instead McConaughey started acting in commercials, before taking a role in Linklater's now iconic coming-of-age comedy.