Why Do Everyone Think They Are Smart Enough ?

I'm unclear about exactly what you're asking.  (Not sure why this is in the category of 'circket" and sports, because there is no reference to it in your question.)

But in general, it hasn't been my experience that people necessarily think they are smart enough.  I find people do gather knowledge they can and do depend on, however, and they may not know that they still have more to learn about something until they encounter a situation in which their current knowledge or skill doesn't help or isn't enough.

I think the more mature a person is, the more they are able to understand that there are always things to be learned.

Are you asking in general terms or in cricket , be clear my friend