The CDC recommends 56g daily for males 19 and up. Out of your daily calories somewhere between 10-35% should be from protein. http://www.cdc.gov/nutrition/everyone/basics/protein.html
That being said, you're correct that it isn't good to rely on one source of protein.
I have two aunts and an uncle, all of whome were vegetarians for over 15 years and then were advised by their doctors to either supplement regularly or go back to eating some meat, simply due to protein deficiency and muscle attrophy, even though they're cyclists and hikers and just generally active people.
Personal circumstance definitely matters too. I work out regularly and over the past 6 years or so I've found recovery to be most difficult, long, and painful if I dont hit my goal of at least 1g of protein per lb of body weight, daily, from variable sources for continuous breakdown.