Have you noticed that we tend to criticise people in great detail but praise them only superficially? If we are criticising somebody — for example, for breaking a promise — we spell out exactly what they've done wrong, how much it offended us, and for good measure we mention all the other times they've let us down.
But what do we say to someone who keeps their promises? If we say anything at all, we might give them a word of thanks.
When we criticise ourselves, we do exactly the same, especially when we're feeling depressed. We knock ourselves in great detail but pay little attention to what we've done right. Interestingly, research tells us that when we're feeling depressed we tend not to remember the detail of events, but to think in sweeping statements, like "I've always been useless at relationships".
Try and train yourself to remember specific details so that good times and experiences are as easy to recall as the bad times. Put aside a little time during the day to make a list of actual achievements and positive aspects of yourself, such as "I'm being sensible with money", or "I helped my nephew with his homework" or "I cooked a nice meal."
Make sure your list also includes details of pleasurable activities. "The new Ricky Gervais comedy really made me laugh." You may well find that your life is richer than your negatively oriented memory lets on.