Depression and seclusion
When you are depressed, you often hear the people around you say that you need to get out more, meet up with friends. This would be “the solution” to make you feel better again. You're not going to hear me tell me that this is bland, but it's really a lot easier said than done.
Goodbye energy!
A depressed person usually has no or very little energy. We get up tired and we go to sleep tired. This is very heavy and immediately dragging all the motivation out of us. We hang out on the couch all day or sometimes we don't even get out of bed. So the fut to talk to other people is also very often missing, let alone actually meet up.
At first, your friends understand you, but soon you will find that their understanding is exiting.

People may not say it directly to you, but it is said that you neglect your friends, that you don't care about them anymore, or even that you're just thinking about yourself. Some of your friends may even think that you don't like them anymore and therefore don't go into their invitations anymore. That you're making an excuse.
This also applies to family and, of course, not just friends. You will visit your (grand) parents, your cousins, your siblings, your siblings,. You would still consider a family gathering, but that also has its consequences.
A heavy mask

If - after a lot of insistence- you still go into an invitation from friends or family once, the uncertainty has been striking days in advance. People are probably going to ask you why they still see you so little and often people don't understand what depression means, which can sometimes make them very rude to you. So you usually shut up or make excuses like “it's too busy in the office”, for example. The reality is, unfortunately, a whole lot different.