It's often overlooked, even by scientists themselves, that much of the light that hits the JWST has been travelling across the universe for millions, or depending on what they're looking at, many billions of years. The universe as we see it today (and as the JWST will see it) isn't actually there. Or at least, much of it isn't there anymore. It doesn't look like how we see it. Looking across the universe is literally looking back in time at how things once looked at the time the light was first emitted from whatever star or galaxy we're looking at.

Of course we can still learn a lot about the universe with the JWST, but if, for example, we find a planet that looks like it quite likely has life on it, there's no guarantee that the life is still there, or even if the planet, solar system or galaxy it belongs to is even still there.

Because of the sheer vastness of space, and the fact that nothing can travel faster than the speed of light - and anything with mass can only travel a fraction of the speed of light - we will never know for sure if we're alone or not. The best we can ever hope for is to find a planet that appears to give off organic signals that indicate life might (have once) existed on it.

There's a reason for the Fermi Paradox (the strange anomaly that given the sheer size of the universe, it all seems so.. dead) and that's because it's simply too difficult (I would guess impossible) to travel the distances needed to ever encounter other life on other planets.

Of course the JWST is just as exciting nonetheless. It will still give us lots of information about the universe, especially its origins, that we haven't known up until now, but I'm not expecting it to prove once and for all that little green men are out there.