I've left a couple, the signs I found were
1) Not being happy in the place that I worked
2) Colleagues not getting along
3) Achievements the company/team had made were just brushed off (even if it were large ones)
4) Management not listening to employees
5) Generally wanting to leave
After I saw these signs I just handed in my letter of resignation and left. I knew that leaving the company would be good for me because it was affecting my personal life. I wrote a bit more about it here dev.to/rapidnerd/string-happyworkp...
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