If I asked you a question about yourself, the answer would depend on what else is on your mind. Your self-image is extremely susceptible to the availability heuristic. This heuristic causes you to assume something is important or more likely if you can easily think of an example of it. So if I asked if you were assertive your answer would depend on how easily you could think of an example of your being assertive.
If, earlier in the day, you had had occasion to think about being assertive, you are likely now to come up with examples very easily. Hence you will answer that you are indeed quite assertive. If you had not thought about it earlier then you will now have more difficulty coming up with examples. You would therefore answer that you are not so assertive.
The same happens when asked about your general feelings. Schwartz, Stack and Mai asked students to fill in a questionnaire. Two of the questions were, “How happy are you these days?” and “How many dates did you have last month?”, well separated within the questionnaire so that the students didn’t consciously link them in any way. Some questionnaires asked about the dates earlier than happiness, and some later.
The answer to the number of dates showed no correlation with happiness when the happiness question came first. When the dating question came first though, those who had had more dates rated themselves as happier than those who had had fewer. When asked about their happiness they thought about reasons they might feel happy or sad. Because they had recently thought about their dating life, this easily came to mind and influenced the assessment of their happiness.