Own responsibility

Aren't people suppose to be responsible on their own job, task that had given or assign to them? Why this people always ask people help them to do their job that are not that person should do? Guys, please! Do not takes things for granted. Each people have their own things to do and time to rest. If the person can help then is ok. But when people tell you no then please do not force that person. YES means YES, NO means NO!