Glory
As with most careers, how you feel about what you're doing is directly affected by the impact it has on the world. Seems a little obvious, right? Think about it, if you're designing and building minute parts for new kinds of lawnmowers, you probably won't be over the moon (though, of course, lawnmowers may be the height of excitement for someone out there).
However, if you're helping to design new safety features in automobiles, new, more structurally sound bridges, or more efficient alternative fuel machinery, you'll probably feel mighty proud of yourself.
Along with your brilliant new innovations come the chance at industry-wide recognition, thanks to awards given out by groups like the Institution of Mechanical Engineers and many others. Being recognized for your work will certainly have an effect on the way you feel about what you're doing, even if it is a more aerodynamic blade for your basic lawnmower. We'll totally use it.