What is the difference between these two words? I always have difficulty using them.

If I say "a common person", do i imply this guy is not talented, of below average ability?

If i say " an ordinary person", do i mean he is just a person of the mass, an average joe?

Does 'common' has a more degrading sense?

For example, if sb make mistakes, should i say to console ' hey man, you are just an ordinary person, not a big deal.' if i use 'common' in this sentence, is there a difference?

thanks a lot, as a newbie, i find this forum very useful and friendly.
Common is an insult when it is applied to people. With most things, it can mean close to a synonym of 'ordinary' or 'widespread' but with people it usually takes this meaning only: common – vulgar, coarse, ill-mannered, rough, low-class, unrefined. So it needs to be used with care.

Ordinary person means exactly what you think.
Both of these words can sound negative, so, using your example, you would comfort this person saying: "Hey man, you're only human, not a big deal." Using the word "ordinary" might be insulting; the word "common" certainly would be!