The only times i have felt lonely is :
a- When i miss my loved ones
b- When there is a communication gap or miscommunication between me and the ones i love.
c- When i am stuck in a gathering where i cannot relate to the people owing to various reasons such as values and interests. If you find yourself in such a place for an hour or more, trust me- you would be lonely and would want (i) the event to finish a.s.a.p (ii) want a friend to walk in.
Loneliness is essentially different from solitariness i.e. in this case, being comfortable with your own self and thoughts and your own company, as opposed to loneliness when you want a loved one to be around you or where you are seeking to communicate or be understood by a certain someone, and the same is not being achieved. You can be lonely in the company of another as well.
Different people have different preferences. i know people who just need to be around folks and go out to feel happy- in the absence of company, they feel depressed. But i also know people, who may be with people, but will be completely aloof and in their own world.
Me- I’m a little of both. I am lonely at times when i miss my loved ones and then there are times, when i just want to be alone , with a good book in hand, a notepad and a pen, and me and my own thoughts. *Bliss.*
Lets face it. we are not all similar. Therefore our needs are different too. For some people, loneliness may not be an introspective phase, they may instead actually suffer from depression.
Loneliness is not essential for self introspection and learning and neither is being alone. It is ofcourse a great opportunity but some people can learn by an event, by observation, by simply thinking and evaluating things. I repeat that loneliness is a negative feeling. if anybody ever feels that someone may be going through that phase, reach out to them- you may be doing a lot for them simply by talking to them.