How to not feel bad when one's ideas are not accepted (by co-workers or bosses)?

A co-worker (and friend) has this "ego-problem."

When he offers ideas in work meetings or up the hierarchy (at work) -- if the ideas are shot down, his feelings get terribly hurt. He feels so bad that he shuts down and eventually stops proposing ideas.

What are some ways in which he can become less invested-in and identified-with whether or not his ideas are accepted? How can he get his ego out of the way? How can he learn to focus on the process (offering ideas) instead of the result (whether said ideas are accepted or not)?