
To know them at work or as an acquaintance, you'd never know someone was depressed. It's hard to spot, and difficult to pin down as a depressed person is actively hiding their symptoms, avoiding scrutiny.
They can almost never shut down their minds
They have endless and uncontrollable negative self talk, self reflection, and self loathing that takes away their energy and makes it hard for them to focus, and to sleep. This "talk" is always inwardly focussed.
They find it hard to trust
They often know many people, but they trust very few. To be trusted is an honour, and means you make the person feel safe - or at least you are predictable. People find it easy to trust them however.
They are difficult to get to know
However they may know you well. Their painful inner life makes them attuned to others' hurt. They will always offer a sympathetic ear, but will rarely be the ones seeking such an ear for tmelselves. They will speak of themselves only superficially.
They are smart
To endure the pain in silence, to avoid detection, to be the listener for others takes an enormous effort, and a lot of skill. This skill is used to build themselves a high wall behind which to live.
They are empathetic
They are very in touch with the raw feelings they have and can't shut down. They can easily relate to feelings in others, and are capable of feeling for others, be it sadness or happiness, and are the first to commiserate or to congratulate.
They make their own lives harder
By not being genuine, absorbing other people's stresses, and not seeking help or treatment, their lives are made so much harder. Their lives are exhausting, and sleep is rare and disturbed.

That depressed people often excel at the very skills that would help them heal is tragic - in that these skills are used to hide, rather than to express.
And it is the exposure of expression that they most fear, is their greatest fear, that the self-loathing will be proven correct and they will be discovered as fraudulent and grotesque human beings. All while being beautiful, sensitive, and generous.
Therapy is a safe place.
it's a place where, if you are depressed, your reluctance is understood, and the pace is set by you. Seemingly tiny steps can be incredible achievements, and glimpses of self compassion are healing.
Therapy can teach you how to trust, and help you begin to live authentically, giving you the ability to live as you would prefer, not as your thoughts and habits dictate. Over time, you can emerge from behind your wall, tentatively, learning the lay of the land, and starting on the path to happiness.