The biggest mistake a leader can make is to not fight enough for their people.
In all of the largest companies, promotion time is a time of in-fighting. It is contentious at Amazon, Facebook, and every highly competitive place. A promotion cycle is when managers literally shout at each other to promote their people.
Only so many can be promoted in each cycle, and far more "deserve it" than get it.
There is no question that emotions have run high in every promotion calibration meeting I have been a part of too, and I have had to fight.
In one particular calibration meeting, the fact that someone I was trying to promote wore shorts all the time came up. The argument against his promo was that "kids" right out of school shouldn't be in senior engineering ranks. The guy had a kid of his own, and far from right out of school, he was an amazing engineer and ready for more scope. He deserved and did get the promotion. In another instance, I had to threaten resignation so a direct report could be promoted.
No matter how ridiculous you think, this is; if you don't fight, you won't succeed.
Teams know when leaders don't fight for people that deserve it. People leave those teams, and other great individuals will not join them. It makes sense that they wouldn't; who would want to be lead by someone that won't fight for their achievements to be recognized and rewarded? No one.
No leader will ever say they don't fight for their people. But, in my experience, the ones who fought the hardest had the best teams in the long run and added the most value to the companies I was a part of. All of this simply because their people gave it their all. They knew their contribution would not end up in the abyss.
When it's time for people's achievements to be recognized the best leaders fight.
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