I have yet to lose a kerbal in my latest career - Most of my ships are unmanned, although I did take a risk with my first mission to an Even orbit being a manned one. Three crew, a big ship, and a safe return to Kerbin with no fuel left after the transfer burn out of Eve, and then two more transfer burns because I don't know how to interplanetary. Ended up tweaking my Kerbin approach using RCS, which thankfully I had plenty of! I've counted that as a rescue on my Eve badge, because I was pretty convinced that they were all goners! But anyway, I also do all my testing using probes, and only once I understand a planet reasonably well do I risk sending Kerbals to give me reports.