This is a common problem. It often stems from not having a good self-efficacy (psych term similar to self-esteem) - essential it is about what you think you can accomplish. When you don't think you can achieve something, you set your goals at unrealistic heights so that when you don't reach them, you can say "well, it was really impossible for me to meet that, so I don't feel so bad". You need to change that negative thinking to positive thinking - you can do this, you just gotta do it in a realistic way. You can always start small, with something that you know you can accomplish, and as you see these things happening, hopefully it will increase your confidence that you can accomplish this overall goal, and you'll start setting slightly higher challenges for yourself. Good luck. We're here to support (and challenge) you!