Here is what I did.

Me too, 小时候，学习不好，每次考完了，心里也是没底，爸爸妈妈还总问。

I felt really frustrated when I couldn't answer their questions. So one day, I decided to make a change. The next time my mom asked, "did you do well?".

I asked back, "what is doing well"?

"Above 90 points."

"Yes, I guess so."

Days later, the results came in. In a notebook, I wrote what I thought I would get (either good or bad)and what I actually got (good or bad). After repeating this process several times, I noticed I got bad results most of the time.

So later when people asked how did you do, I was able to answer them with great confidence from the bottom of my heart, "not very well".