Why I reject a compliment before I've even said thank you
The pattern, in five beats
Someone says 'that was really good, what you did' and before the sentence is finished, you've already answered 'oh, it was nothing'. You didn't decide that. It just comes out on its own.
What I say instead of thank you
'It was nothing.' 'I got lucky.' 'Anyone could have done it.' The words arrive before you've had time to choose them, as if they were waiting right behind the other person's sentence, ready to come out the second it stops.
There's often a heat in the face, the eyes sliding off to the side, and the first thing you do after is ask the other person how their own day went. As if the compliment were a ball you had to throw back right away, before it could stay in your hand too long.
The sentence I heard before that one
Often there was a table, earlier, where an achievement was followed by something else. 'And how's your sister doing.' Or just a silence, a bit too long, after the good grade was announced. The compliment never got to finish on its own, it always opened onto a comparison or a putting back in place.
So minimising became a kind of insurance. If you say yourself that it was nothing, nobody else needs to say it for you, and nobody can take away something you never claimed to have.
What I will not tell you
People will tell you to learn to say thank you, just thank you, without adding the sentence that erases it. That's not wrong, but it's not what I'm going to tell you, because it assumes the reflex changes by being corrected, and that's not how it works.
What shifts is something else, smaller and more solid: the moment you feel the minimising sentence starting to rise, right before it comes out. That's not stopping it yet. It's just seeing it coming, once, without doing anything else with it.