I'd talk about the correlation between savings percentage and years to retirement (MMM's shockingly simple math post), and about how standard retirement advice has people set to work 40+ years. IMO this is the most basic foundation of personal finance that once understood can make the largest difference in how someone views money. Everything else follows from this.
Since it's mostly people just starting out in their career, I'd talk about how just because they're excited and love what they do now, they'd do well to assume that's not always going to be the case. At some point they might want out, and having that option is invaluable. I'd also discuss how it's assumed that you have to spend everything you earn for maximum happiness, and how that's proven over and over again to not be true, and how if they increase their savings as their income rises, instead of increasing their spending, this will give them options and freedoms in the future that most people won't have, and this HAS been shown to increase happiness (has it? I'm assuming it has but not positive. Either way, they don't know).
I think for the most part people don't know why they should save, or they think saving more would reduce happiness, so for anything else to get through, you have to get over that hurdle first.