I agree. The biggest reason why employees (or hell, founders too) quit is because they don't feel appreciated.
If I'm working 60-70 hours a week and have a never-ending stream of people inside the company griping at me about why I wasn't able to get non-essential-to-my-role task X,Y, or Z done for them (this is what being in a big company feels like) - that really starts to mount even for employees who know that they're appreciated by their immediate peers and leadership.
Being appreciated by your managing team or your peers isn't enough - YOU need to feel like you're doing a good job. Even someone with a stalwart self-sureness will crumble if they feel like they're constantly failing to deliver what the business needs.
It's about more than just feeling appreciated and feeling like you've done a good job.
I had both, and yet I still burnt out.
What was lacking was fulfillment -- the sense that the work you do is meaningful for you.
Ideally, your job should be interesting, fun, stimulating, and you should feel that what you do is important. If it's stressful, it should be at a level of stress you can deal with, and the stress should be of a positive sort, not a negative sort.
At some of my jobs I was greatly appreciated, and I knew I was doing a great job. But the work was boring, I didn't feel it was important, and it was extremely stressful. So I burnt out.
If I'm working 60-70 hours a week and have a never-ending stream of people inside the company griping at me about why I wasn't able to get non-essential-to-my-role task X,Y, or Z done for them (this is what being in a big company feels like) - that really starts to mount even for employees who know that they're appreciated by their immediate peers and leadership.
Being appreciated by your managing team or your peers isn't enough - YOU need to feel like you're doing a good job. Even someone with a stalwart self-sureness will crumble if they feel like they're constantly failing to deliver what the business needs.