As writers we have a requirement to express emotions through our characters. But, what do you do when you don't know how something feels?
As a depressive I can write about that aspect of life relatively easily, albeit painfully. But that's from a man's perspective. Is it the same for a woman? Judging by Sally Brompton's book, Shoot the Damn Dog, yes.
Is it true of all things? What about being an immigrant? Can any of us truly understand that experience?
Research will only cover so much, listening to others will uncover much more, but nothing will replace actual experience.
One example is from a friend of mine who wrote a fantasy book, sadly no longer available, in which there was a fair bit of swordfighting. Her descriptions of it were scintillating, mostly due to the fact that she had taken part in medieval sword fights while training as a knight. I kid you not. There are schools in Britain that will teach you jousting, sword fighting and a number of other medieval fighting arts.
Lucy had a lot of experience to draw on, so when writing those scenes they came alive in a way few other writers could match.
I can write about I.T., homelessness, despression, raising special needs children and a number of other things, all from personal experience.
Life on another planet? What environment would you be living in? Put yourself there.
Living as a man or woman? Try to imagine the small things, like living with different body parts.
Unless you are living, or have lived, as the character you're writing about you will never know for sure what goes on in their head. With some decent research and an imagination, you can get closer than most people and deeper than you think.