This is a great question. Sadness is one of the basic emotions we feel. It’s normal to experience feelings of sadness in response to adverse life events. Throughout life we experience many situations that can make us feel sad. However, feelings are different for everyone and everyone reacts to a situation differently. A situation might seem trivial to one person but may be really important for someone else. Some people can also have difficulty in identifying sadness as an emotion due to their culture which values positive emotions over negative ones and where sadness is considered a sign of weakness.
If you feel like you are supposed to be sad, you have to figure out what is making you think this way. Did something happen in your life like loss of a loved one or disappointment/setback and is sadness the appropriate emotion for you to be feeling at this time. You can also ask yourself what a particular situation means to you and what emotion is appropriate for that situation. If we take the loss of a loved one as an example we see that everyone reacts differently to the loss (even within one family). Some people might grieve and feel sad for a longer time whereas another person might feel sad for a short time then move on with their life. Both of these responses are natural human responses and both are okay.
If you do find yourself to be sad, understand that it is okay to feel this way. Feeling sadness is part of being human. You could be feeling sad for many reasons. Allowing yourself to feel sad is not a bad thing or sign of weakness at all. You don’t have to be positive all the time, allowing yourself to be sad enables you to appreciate the good things in your life more. If you allow yourself to be sad you can also explore and understand what you need to help you get through this emotion which could include many things like talking to your friend, going out for a movie or having time for yourself. Finding out what works for you and helps you cope with sadness can be really helpful and you can use this knowledge to help you cope with sadness in the future as well. These things can also help you in trying to make yourself feel happier when you are sad. To feel happier when you are sad, you can also engage in things you like to do (like hobbies) which could include listening to music, drawing, exercise etc. You will enjoy doing these things and it can make you feel happier.
Sadness is transient and does pass. It can pass quickly or it may take a longer time to pass. However sometimes sadness can deepen and become chronic. If you find this is happening to you it might be a good idea to seek help from a professional (doctor, counsellor, psychologist or other healthcare professionals).