Researchers may nd certain practical difficulties. Imagine that you are doing a survey as part of the research. First of all, you have to get enough copies of the questionnaire. For this you need money, time and efforts. To distribute the questionnaire among the students you will need permission from their teachers. The first time, you may be denied permission. You may be asked to come back at a later date.
Even if you distribute copies of the questionnaire, many students may not fill them and return them. Sometimes they may leave some questions unanswered. Then you will have to decide how to solve. the problem. Or you may take only those copies which are fully answered, and reject those which are only partly answered. You should be able to face any problem that might come up during your research work.