You live only once The logician would argue, You only live once should be rewritten as You live only once, with only next to the thing it qualifies, once. The logician would be unbearably pedantic, but there is a grain of good taste in the pedantry. Writing is often clearer and more elegant when a writer pushes an only or a not next to the thing that it quantifies. In 1962 John F. Kennedy declared, “We choose to go to the moon not because it is easy but because it is hard.” That sounds a lot classier than “We don’t choose to go to the moon because it is easy but because it is hard." Steven Pinker, The Sense of Style grammar
The observer effect In biology, when researchers want to observe animals in their natural habitat, it is paramount that they find a way to do so without disturbing those animals. Otherwise, the behavior they see is unlikely to be natural, because most animals (including humans) change their behavior when they are being observed. Farnam Street fs.blog The Spoken and the Unspoken uxethnography