It’s a matter of practice to work out which ones to note down, which ones to let flow. I find that an idea that someone else tells me will make a great story seldom sticks with me – not because it’s a bad idea – but because it’s not speaking to me, it’s speaking to them. There are exceptions, but not that many. As mentioned before, I tend to note down anything that sounds interesting or silly or rhythmic or curious without examining why it appeals to me. If it’s meant to be something more, that will be revealed later when I come to reread my notes.
This reminds me of Austin Kleon’s work.