What is so wrong with being a “Know it all”?

So what if I happen to understand how most things work or don’t work – or how to make most things or how to remake something to fit a new purpose? And what is wrong with letting people know about it?

If I see something broken and fixable I will often just fix it and go on. Sure you can take your car to the garage and pay them $135 just to look at it but I would rather look at it myself – figure out that it will take a $40 part and about as long to install as the trip to the garage.  What is so wrong with mentioning that? And if there are two possible causes of the problem and the $40 part is not the cause? Then take it to the garage and pay them the $300 for the more expensive fix? I would guess that my method saves me at least a couple thousand a year just on auto repairs.