Stop saying that you are not good in math. This is negative thinking.One major reason is that it's generally difficult. Let's be honest. Not everyone can calculate advanced mathematical equations. And the majority includes me. I like math for what it is and its importance in life. But I'm far from being good at it.
Another factor is the fact that it pressures people. It puts them on the spot of a reward or punishment situation. If they're able to do it and get it right, they're applauded. But not knowing and making a mistake yields an equivalent negative reaction. Be it from teachers or their peers.