Magnification is when you blow negative things way out of proportion and minimization is when you shrink good things down to almost nothing. For example, you are trying hard to reduce the amount of time you spend reading news and social media on the internet and you end up, one Saturday morning, spending 45 minutes online instead of the 30 you planned and you think, "Agh! I blew it! This is terrible! How awful! This is so, so, so disgusting I can hardly stand myself! That afternoon you spend three hours helping a young family move their furniture into their rented moving van, including wrestling their upright piano with five other guys down a flight of stairs. And when the mom in the family stops and expresses appreciation for all your help you say, "Nah. We didn't do much," and on the way home you berate yourself for being such an ineffective help when you are sure there are so many other people in the world who do so much more than you do to help their neighbors.
If you magnify all your errors and minimize all your good work, of course you are going to go through your days feeling like a loser or a failure, or at the least, quite hopeless about your ability to become who you wish to be. But the problem isn't you. Most of us, including you, fall within the normal range in our mixture of good choices and not-so-good ones. The problem is the lens through which you are viewing your particular mixture.
And that can be fixed.