I can think of two reasons: inequity aversion, and chance of reward.
If colleagues are getting the same pay for less effort, that’s unfair and it’s human nature to even things up by working less hard. And if everyone on your team is working hard, that team is likely to succeed and the employees to be rewarded, so there’s an incentive to work hard yourself. If everyone else is slacking, your efforts are unlikely to make a difference, so what’s the point? This is even more the case in a small business like the restaurant.
I have a similar sort of job. Really, with our jobs, it’s more about creating an environment that allows the various members of our teams and other reports to be as effective as possible in their jobs.
Really, at my level, I’m kind of beyond “basing my LOE on what other people do”. My job is really more about supporting and to an extend defining the culture of my firm. Do we want this to be a place where the expectation is our consultants work crazy hours to get the job done? Some firms I worked at didn’t care and expected you to drive the team. My current firm does care, so we have to create a business model that encourages regular work schedules. Not just managing employees behavior, but also how we scope projects and set expectations with our clients.
IOW, driving my team to work 80 hour weeks doesn’t show I’m “putting in extra effort” because that’s not our culture. Putting in extra effort in this case is working with sales and other groups to make sure the projects are properly scoped and then quickly addressing issues with the client if it appears our consultants are overworked.