Anyone can say that he is great and a lot of people will believe him. He can say that he have a lot of houses, cars, medals, trophies, money, wives, achievements etc. He can say that and some fools will buy his stories. Some fools will be amazed at him and treat him as a royal human being.
I don't know why people do it, maybe they feel good about telling their fantasies that they know will never come true because they know themselves... all they can do is talk about something and not do anything.
But the thing is this.. you can only fool people once but not twice. You can promise them anything, you can make them believe that you are great but once they learned that you're just a joke... then next time they won't believe you anymore, they won't even bother to talk to you.
To make a person believe you forever, you should show him some evidences that you can really do it or your really have it or else... He will just laugh at you next time you tell him your make believe stories.
A lot of people nowadays were jokers. They will state facts, give advises that they cannot even do themselves. I don't know how they were able to stitch stories about success and make people believe them. Maybe it is their talent to tell lies. But that talent will just work once. Once your true colors is revealed that you're just a liar... People won't respect you anymore, people will see you as a crazy or something. And even if you produce some little success... they will call it a fluke or luck.
So you better back up what you say, you better prove them that you are for real. You have to show them real evidences not just verbal evidences.
People nowadays were smart, they were very good in detecting who is fraud and who is legit.