Most of the people in this world just trudge along in their day to day life. They cling to their job without thinking much even if they don’t like it.
But smart people think in future. First of all, they think about what they want to do in life. Then they figure out if what they are doing day in and day out is what they actually wanted to do in life. If they figure out that the things they are doing is not what they wanted to do in life in the first place then they plan ahead. First they set their goals for the next 3-4 years. Then they figure out how to achieve that goal. Once they are certain about their plan then start executing their plan. they make learn new skills, find out right people and network with them. they set smaller feasible goals in smaller time frames and achieve them one after the other. In the end, they succeed in their effort and reach to the goal which they had hoped and planned.
This is the biggest difference in smart people and not so smart people.
Sometimes, even if a smart person is happy in its present job, some outside events may lead to situations which are not likable. For instance, the company is acquired by some other company and management is changed. The new management may have its own goals and you are supposed to work on things which you do not like or do not want to do. Such instances, forces you to think about your options and your future.
Again if you think smartly and plan your career then you can quit your job and pursue your goal successfully.