We each tolerate different levels of discomfort and inconvenience to prevent others from being unhappy with us. Neither extreme makes sense. People who demonstrate little willingness to compromise are selfish. And, people who contort themselves to avoid imposing on others, and thus avoid confrontation, are allowing others to make decisions for them.
Fortunately, standing up for yourself doesn't preclude compromise. In fact, often you can do both. But, people who haven't asserted themselves much in the past tend to overcompensate.
In personal settings, both people in a relationship should feel comfortable speaking up for what they want and should also be ready for some give and take. And at work, the sign of a good negotiation shouldn't be getting away with the fewest concessions; rather, it should be that all parties feels like the ultimate agreement leaves them better off.