Hello and welcome to the intelligence from The Economist. I'm your host, Jason Palmer.

Every weekday, we provide a fresh perspective on the events shaping your world.

One of the trickiest social norms to navigate away from home is tipping.

Is this too much? Too little?

Turns out that it confounds economists too.

We look into the motivations for the tippers and for the tipped

and how that affects businesses overall.

And now that the saga of Novak Djokovic's Will He Won't He at the Australian Open has been resolved,

we take a look at why the Serbian is an outlier among elite athletes,

and some surprisingly long-run effects that sports stars suffer after COVID-19.

But first...

Net zero emissions commitments are spilling out of businesses and even governments all the time these days, but the latest one is kind of surprising.

ExxonMobil, America's biggest oil company. It's got a pretty checkered history on climate matters, from executives that denied the

role of fossil fuels in climate change to allegations of disinformation campaigns, which

generations of those same executives have denied. But now there does seem to be something

of a change of heart going on. We've seen a significant shift on climate change from the most important oil company in the Western world, ExxonMobil,

one that has actually historically been quite an opponent of action on tackling greenhouse gas emissions.

Vijay Vaithi Suaron is our global energy and climate innovation editor.

They have just announced a policy which aims to get the company to net zero greenhouse

gas emissions by 2050.

But more importantly, I think they've also taken on concrete targets for absolute levels

of greenhouse gas emissions, promising to cut them by roughly 20% by 2030

...