The 8th principle of the Agile Manifesto is

Agile processes promote sustainable development.
The sponsors, developers, and users should be able
to maintain a constant pace indefinitely.

At a previous employer, I remember a coworker of mine. Let’s call him M.

M was a good guy, capable, and hard-working. He always put in what was required, and often more. On one particular project, there was a deadline coming up, and his team wasn’t going to make it. So, he buckled down and put in over 100 hours that week to make sure that they got everything delivered. Then the deadline got pushed back, giving them a bit more time, but he had to put in another 100+ hour week. Then the deadline was pushed again, with the same result — another 100+ hour week. He didn’t even go home, he’d just go to sleep under his desk at night, then climb back into his chair and keep working (except for 2 showers each week). This kept happening for a number of weeks until he gave up and left the company.