SOHO has far outlived its planned lifetime and in fact has achieved something unprecedented so far as I know, starting out as a scientific research satellite and ending up as, effectively, an operational space weather satellite.
But, yes, space is a very harsh environment, and every spacecraft is going to fail eventually. Most are only designed to last 3-5 years, though since they have an extremely high probability of lasting that long, there's a respectable probability of lasting significantly longer. Most NASA spacecraft either fail very early on or last quite a long time - there's not much intebetween.
Everything I need to know I learned through Googling.