I'll be very honest, medicine isn't as great as everyone thinks it is, especially in the UK. My reasons for continuing with it now are that 1) I'd get bored to death if I did an ordinary office job, 2) I've invested so much time into this now there's no way I am backing out, 3) it's stable and gives you many opportunities.
All the "saving people" stuff gets knocked out when you see the realities of day to day life as a doctor... Sad, but true.