Accidental Existing Melodies

[IneptWizard]

Hello, I would just like someone's opinion about something. So I find it very hard sometimes to find a melody that sounds good but hasn't been used before. Very often, when I find something good, I realize what song it's actually from. But... it's not always a long melody. Sometimes just one bar of 4/4. So my general wonderment is this: If I'm writing a melody, and one bar is similar to an existing song (we're talking about 3 seconds of similarity here), should I just use it as long as the other parts of the melody are different than the song in discussion or am I being an extremist of originality?

 

Thanks!

[IneptWizard]

Thanks for your replies! I think I know what to do. Also I might add that when I have some lyrics ready, the melody changes a bit depending on the syllables of the words. So it might not turn out as similar as it did to start with.