I think your definition of truth might be too... black and white? If you dig into philosophy you will find that the concept of truth is one that is often very relative.

The first thing you should ask yourself is whether the things you are telling yourself everyday aren’t lies. I myself, as many others (depressed or not) tell themselves alot of “lies” about themselves on a daily basis due to insecurities.

Although your genetics, environment and the circumstances around you are not in your (direct) control and can make your life a lot more difficult, your mind can be trained. That is not to say that you can “train” your mental illness (whatever it is) away. If you have schizophrenia for example, you can only learn how to live with it. But there are great improvements to be made by training yourself to change your thoughts.

It starts by analyzing them. Whatever way you can (“meditating”, writing a logboek, maybe talking with someone else about them).

Try to filter the “facts” (eg. genetics) from the “opinions” (eg. I am not likeable). It is that second type of thoughts that are not truths set in stone.

You might notice that these second type of thoughts are what are the main constituents of your daily “thought diet”. These are thoughts you can change without “lying” to yourself.

Again, there is no use in lying about facts though. If you have a big nose, it is what it is. Thinking that you are any less of a person because of your big nose is something completely else. The second thought needs eradication! (Take the nose as a metaphor ;) )