That's a good point, but I'm not sure the belief you describe is one held by all, or even most, scientists. Science in actuality is all about uncertainty, error and approximation. No experimental result is ever published without a margin of uncertainty or some kind of lemma or disclaimer; "We found evidence/found no evidence for [some hypothesis] at 95% confidence level". I think (though this is a hunch) that a lot of scientists believe something more along the lines that knowledge gradually becomes a better and better approximation to the truth - you could almost say that rather than getting better, our theories get 'less wrong'. But it's asymptotic; science converges on Truth but never quite gets there. There could well be aspects of the natural world that, even in principle, we can't satisfactorily investigate. A good example is physics at the Planck scale, which in order to probe directly in the standard collider paradigm would require a VVVVVLHC the size of the galaxy.
An unshakeable belief that science will one day explain everything sounds more like an attitude you might come across in lay 'science enthusiasts', rather than actual scientists. People who were all over the internet with their "OMG Einstein was wrong!!!" when the anomalous CERN neutrino results were published (or rather, released in a preprint), instead of thinking "Well, it would be fascinating if true, but it's probably miscalibrated instrumentation and doesn't mean much until it's been confirmed".
I don't mean to sound snobbish about this, I'm just saying that if your main source of information about science is Brian Cox on the telly and a shelf full of books by Hawking, Dawkins, Steve Jones, Brian Greene etc. then you might well think science is all about earth-shattering discoveries and paradigm-changing theories, without realising that 99% of the time it's about painstaking analysis, theoretical dead ends and the gathering and processing of lots and lots and lots of very, very, very dry numerical data.