It is usually only "allegedly". It's not a universal law but comes from the world of quantum physics, where it can apply.
It depends on what you are observing, and how. If people know you are observing them they may not act as they normally would even if they don't object. If they are politicians or "celebrities" they might even exaggerate their actions for effect.
Similarly you won't be much of an ornithologist if your bird-watching disturbs them.
On the other hand, observing the actions of a piece of machinery, say, won't affect it unless the test is designed to take it outside its normal range - and might break it.
You may know by now Durdle the world of Quantum Physics fascinates me. Had I the brain for it that would be my chosen profession. I've read/own a bazillion books and have no educational background. But I'm always drawn to things like quantum entaglement or black holes or multiverses or the question of what is reality really? I don't understand everything I read but that doesn't stop me from reading it. That entire world has endless potential and possibilities. One could not possibly be bored being a Quantum Physicist. Which brings up a question I shall ask. Shroedinger's cat...is the cat alive or dead? I'd much rather talk about the depth of the Marianas trench or what is happening to the great barrier reef than about politics. Politicians are uniformly one-dimensional and very boring. An aside for what it's worth. Quantum physicists keep seeking truth and it is always elusive. I just thought of another question. Thank you for your thoughtful answer. My brain is constantly thirsty to be sated with information about star stuff. That's what Carl Sagan told us decades ago. "We are made of star stuff". :)
This post was edited by RosieG at April 14, 2020 3:56 PM MDT
I watched that show last night, too. Quite fascinating. Here is how I learned it. Particles have both a momentum and a position. At the quantum level, particles are so tiny that any instrument that tries to observe and measure them will add energy to the system, thus changing either the momentum or position. You can't measure both of them. Heisenberg's uncertainty principle. This is an oversimplification.
Durdle 