eat one's broccoli
When someone has to suffer through something gross just to get ahead, they've eaten their broccoli.
My cousin got a promotion by cleaning toilets for a year. He ate his broccoli, and it was gross.
That guy worked at a gas station for 10 years just to get a better job. He ate his broccoli, and it was bitter.
She had to endure a whole month of insults from her boss just to get a raise. She ate her broccoli, and it was a nightmare.