This is a phrase often said regarding talents we have been given. Some say you need to use/practice your talent or it will be taken from you or it will somehow be "lost."
I think I'm going to use this reasoning and start telling people "Yeah... I used to have such a knack for astrophysics. Yeah, i was really good. But then i didn't really use it and i guess i just don't have it anymore."
"I used to be such a great artist. I was amazing, I could draw anything. But yeah.. i stopped drawing for a while and well..."
"This reminds me of when I used to create algorithms for fun. But wow, i haven't done it in such a long time and, well, you know what they say..."