People tend to have higher recall for the start of things and the end of things than bits in the middle. The tendency to remember the start of things is the "primacy effect," and the tendency to remember the end is the "recency effect."
Consequently, the start and end of a presentation are rather important, because that's something people will tend to remember no matter what you do. This is both a blessing and a curse, since you don't have to work hard here. If you summarize your talk at the opening and closing, people will tend to get the message and you don't have to do a lot of work to get their attention and have them remember it. On the other hand, if the opening or closing do not go smoothly... they'll remember that, too.
I first became aware of how screen writers approached pacing by an article about Malcolm Hulke, who wrote a lot of television in the 1960s and 1970s. Indeed he wrote a book about it. Hulke argued that a story should be W shaped. You need something at the start to get the audience's attention, and a big finish -- which is perfectly in line with the U shape of memory recall.
The place where you have to do the most work is in the middle.
After a few minutes, people's attention starts to drift. It's in the middle of a presentation that people are less likely to be engaged. You have to do something to bring them back on board, and keep them engaged. This is the middle peak of the W. In a presentation, there are several things you can do. Change the pace or the tone. Do the unexpected. Do something to refocus the audience's attention. If this was a movie or a TV show, you would have a car chase, plot twist, or a dinosaur appear.
This discussion from a Nature podcast is, I think, another variation on the "W" scheme:
Focussing in a way on the idea of mini-cliffhanger this seems to be a thing that lots of good movies have in common. If you imagine Bruce Willis making his way through the skyscraper in Die Hard, he has sort of intermittent battles with the terrorists, which kind of comes to our head at various points and then things calm down a bit and then a new cliffhanger builds up and he gets into another fight. ...
(W)eirdly enough that pattern also seems to happen in Casablanca, if you imagine, Humphrey Bogart and Ingrid Berkman's characters. They are not fighting obviously, but while they are in a way, they're, sort of, wrestling with their feelings and they are, sort of, drawn together and then apart and together and there is a, sort of, mini-cliffhanger's feeling there(.)
A "mini-cliffhanger" is one way to create that middle peak of the W.