"investigate further" is the sticking point.

You're swimming in the ocean and notice something beneath you. Is it a friendly dolphin or a dangerous shark? Do you hold your breath and do a deep dive to figure out which it is? Keep in mind the deeper you go the greater the chance that you'll drown.

It's a strained analogy but I think it gets at the problem. What if you dive a little bit deep - some minor test - and still aren't sure? Go deeper - a more invasive dangerous test - or go back to the surface?

And what if you dive and are pretty sure it's a shark? Swimming all the way to shore (i.e. cancer treatment) is very risky but the shark will almost certainly kill you. How sure are you, really?