It's not always bad to show off. You want your recognition, appreciation, and celebration when it's due, but it's not always fulfilling.
Sometimes you may boast with bad intentions subconsciously, to feel better than someone else. Sometimes you may boast with good intentions, but it's received the wrong way.
When people don't respond how you'd like or expect it can devalue the matter. By being humble we recognise and appreciate our own efforts which is most important. Our intention behind anything should never be to impress.