He always thinks he’s right.
The princess is always correct and the prince is always wrong.
If you want to open the door to my heart, you need the right key, baby.
Ending with an い tells you that this word is an い-adjective. So since you know that the kanji 正 means "correct," what is the adjective version of that word? Well, it's also correct.
This word uses a reading you didn't learn from the kanji. You have to remember the ただ portion in order to read this word, so think about it this way:
After you get the answer correct a clown jumps out of nowhere yelling "TA DA!!!" Imagine it scaring the crap out of you, too.