I will go back and see why this happened and what the mistake is. If your are asking if I am serious about mistakes, I can say working and making mistakes go together. You cannot do the right thing all the time. But the most important thing is to not make the same mistake. That means you have not developed if you still make the same mistake again and again.

สงสัยว่า  But the most important thing is to not make the same mistake.  
ควรจะเป็น  But the most important thing is not to make the same mistake.  หรือปล่าวคะ  ขอบคุณค่ะ