Nobody wants to feel taken advantage of, especially at work. But this can happen if you’re not careful about it. They will look at what you’re already doing and ask for more. There is a certain amount of leeway you should give, since you want to step up for a challenge. But there is a fine line between pitching in when you feel like it’s needed and taking on way too much for no reward. It would be smart if employers always knew to reward their employees for everything they do. But they don’t always do that. Sometimes, they just want to see how much they can get away with. 

This becomes especially easy to spot when another employee leaves the company, and your team is left to figure out how to divide the work. The smart thing would be to hire somebody else. But as employers know to be true, it’s much cheaper to give more work to an existing employee than it is to hire somebody else. But you should give them some reward in return.