When you cannot do something, you may have a default negative thought about it.
You may say: "I couldn't get it right, how unable I am" or something like that and get disappointed and frustrated. The disappointment and frustration is due to your perception.
To feel good, you need to change it.
What should you say then?
The key: Always focus on the positive. In the current and in the future.
Precaution: Do not compare yourself to others.
For example, if you are writing a paper and wrote a paragraph instead of two in half an hour, instead of saying "jeez, I only wrote 1 instead of 2". Say instead "hey, I wrote 1 paragraph, how cool is that!"
The thing is you can always find negatives and positives. Since negatives lead to bad feelings, why not focus on the positive? You have to focus on something and you need to choose. So, choose positive.
The fact is that this thought changing process is itself an exercise and you may fail in it, too.
It is recursive but it is not enough to stop you from changing it.
The key of the key: You could always, ALWAYS, find something positive about the situation. ALWAYS. Believe this and prove it to yourself (i.e. find evidence).
That will create a source of unfinishable energy of positivity.
There is a positive aspect common to all situations. If you don't find a positive aspect on your own, use this common one by default. It is as follows: Suppose you tried everything you could and it didn't work. Then, the fact is this: You are so good at disappointing yourself. Actually, this is an amazing ability.
It takes time and practice for someone to learn how to disappoint themselves. In fact, you add to your practice every time you do it! But, focus on the positive. You are so able. You are able to "disappoint". However negative the outcome, you couldn't get it without the skill. So, since you got the skill, you are able to be skilled.
You can use this as follows. So, when you cannot do something and you have negative thoughts to disappoint yourself, think:
"Hey, I am so good at disappointing myself with my negative thinking.
I am so good that I can do it instantly. Wow! Amazing ability! I'm so able and practice it often.
I cannot imagine what success I would have if I could use this ability to benefit myself.
If I could make myself happy, persistent, confident, wise, etc. by using this ability of doing it over and over (persistence) and practice it, I could proceed so much into the things I want."
Stop here. You have already accomplished something!! You already did something good to solve the problem, a step toward what you want! Recognize that and appreciate it:
"Wow! I can't believe but I did it. I recognized the negative thought and recognized my ability to persist and practice. And I know this is a step towards getting what I want. I already did a step. That's wonderful."
However small, you always, ALWAYS have the RIGHT to appreciate it. Use it! Go ahead and appreciate everything you do good. There is nothing you could do that is all bad. So, you are actually safe. This method works in all circumstances because you can always find something positive; ALWAYS.
An icing on the cake is downward comparison with yourself.
Sometimes you can do this and sometimes not. It's ok. Use it whenever appropriate.
For example, if you write 1 paragraph instead of 2 in half an hour, say:
"Hey I wrote 1 paragraph. It is better than 0. I could have written nothing. But I didn't. I actually wrote 1 (stress it here), 1 paragraph. Amazing."
Does it sound silly? Then, the more you should do. You can also say then:
"Wow. How silly this is. I am so able that I can do it even if it sounds silly. And, it works!!!" And it does, doesn't it? If it doesn't, it will. Keep doing it.
When should you start incorporating negative aspects into your thoughts (to make the learning process faster by using it as feedback)?
Only when you have enough energy, i.e. high self-esteem.
Until you get there, ignore negative things. They won't benefit you.