Both, a new favorable idea as well as an opposing thought should be noted down.
You think of a new feature for your application; a more usable design for your website; a new investment idea; a new blog post; a seminar that your read about…the key to their execution lies in making a note of them.
Darwin wrote in his autobiography:
“I had … during many years, followed a golden rule, namely, that whenever a published fact, a new observation or thought came across me, which was opposed by my general results, to make a memorandum of it without fail and at once; for I had found by experience that such facts and thoughts were far more apt to escape from memory than favorable ones.”
Darwin emphasized even more on noting down opposing or unfavorable thoughts. For a split moment, your mind might ask - can the hard-disk crash; do I have a backup of all my digital pictures; can the seats become unavailable; can there be down-time…if a note is not made of these thoughts then they might just escape, or even worst, you might end up satisfying yourself that it won’t/can’t happen.