I’d always sucked at those.

[Tinkerbell]

As I walked, I thought about what Dad had said. I’d only had my powers for a few years, but they were a part of me. For the first time, I admitted to myself that the thought of slashing the magic right out of myself—and maybe dying in the process—scared the heck out of me.

But I couldn’t go through life as a ticking time bomb either, and no matter what Dad said about “fine-tuning” my magic, as long as I had powers, exploding would always be a very real possibility. Somehow, my whole existence had become a really complicated word problem.

I’d always sucked at those. ??

 

[Pedroski]

The slang meaning of 'suck' is to do fellatio, perform oral sex on a man. This is/was regarded as bad or contemptible. So 'sucks' means 'bad'.


I’d always sucked at those. = I'd always been bad at those (kinds of problems).